Borate And Ph Balance Sticky?

[dlleno]

Hi. is there a pointer to an article holistically describing the pH balance process throughout the water lifecycle, when borates are used as a buffer? for chlorine and Bromine spas at least. I see the recommended numbers but what I"m interested in is a more detailed write-up covering prep, where to buy, when to heat, when and what to add, and how to maintain pH from startup to drain . forgive me if this is already covered; I haven't been here very long and just trying to soak up all the infinite wisdom I see here.

[chem geek]

There isn't a sticky dedicated to borates or pH control. The general order to get things into balance after a fresh refill is the following (this presumes you have a proper test kit such as the Taylor K-2006 for chlorine or K-2106 for bromine):

1) Add disinfectant. For a fresh refill, for chlorine you would add Dichlor. You can use The Pool Calculator to calculate dosages. For a clean spa, you can start by adding 5 ppm FC, but if the spa is brand new or has not been used or maintained in a while, then consider a decontamination procedure using Spa System Flush or Ahh-Some.

2) If you plan to use the Dichlor-then-bleach method for chlorine, lower the Total Alkalinity (TA) to 50 ppm. You do this by adding dry acid and aerating the spa so running the spa jets. The acid lowers both pH and TA while the aeration raises the pH with no change in TA. So the combination lowers the TA. There is a sticky on this called Lowering Total Alkalinity Howto, Not Just For Pools! If you plan on using bromine or only Dichlor (no bleach), then you may not need to lower the TA as much and a TA of 80 ppm may work for you if you are using bromine tabs.

3) If using chlorine and the Dichlor-then-Bleach method or if you want more pH stability when using bromine (especially when not using bromine tabs or MPS), add 50 ppm Borates, preferably using Boric Acid. You can get boric acid from The Chemistry Store, AAA Chemicals or DudaDiesel. It takes around 13 ounces weight of boric acid to get to 50 ppm borates in 350 gallons. Again, you can use The Pool Calculator to calculate dosages.

4) After adjusting the TA and adding borates, then aerate to raise the pH if needed or use some acid to lower the pH if needed. A pH of 7.5 is a good target in general, but for the Dichlor-then-bleach method after switching to using bleach you may want to target 7.8 instead if the pH is more stable there.

It doesn't matter if you heat the spa before or after the above adjustments, though maybe the lowering TA procedure might go faster if the water is heated since this may increase the rate of carbon dioxide outgassing. As for ongoing maintenance, check the pH and if it tends to rise over time, target a somewhat higher pH level such as 7.8. Add acid (usually dry acid) to lower the pH. If the pH tends to drop over time, then raise the TA level (if doing the Dichlor-then-bleach method, don't adjust the TA until after you've switched to using bleach since Dichlor is net acidic). Usually you don't need the TA above 80 ppm when using bromine tabs, MPS or Dichlor, but if the pH still tends to drop you can raise the TA further but I wouldn't go above 120 ppm especially if your CH is high (especially if its above 150 ppm due to your fill water).

[dlleno]

ok this is good. actually its awesome. FYI my fill water is rather good on the nuymbers: 100 ish CA , 90ish TA, and pH near 8 when heated. .

To summarize:

1. sanitizer

2. TA to 80ppm for bromine (I'm not using tablets).

you didn't mention pH here but I assume you want pH in the slightly high region before adding the borates?

3. Boric Acid

4. final pH adjustments

[chem geek]

You'll adjust the pH after adding the boric acid so the starting pH isn't critical. If you start with 7.5, you'll probably end up at 7.2 after adding boric acid. If you start higher, you won't get down as low but it's no big deal as its easy to raise the pH by aerating.

[dlleno]

Is borate level maintenance and periodic testing needed? If so what is the recommended test method?

[chem geek]

The borates don't break down or go away so if you add the desired amount after a fresh refill you won't need to retest it -- assuming you aren't using 20 Mule Team Borax to raise the pH for some reason. If you do want to test the borate level, the LaMotte InstaTest Borate test strips are decent to use for this purpose.

[dlleno]

The actual borate level must not be that critical then if maintenance isn't required even after replacing evaporated water. Given 50ppm target what is the tolerance range for good results .. 45-55? 40-60? And what is the effect of going too high?

[chem geek]

When water evaporates, the non-voltatile chemicals in the water such as borates do not evaporate with it. So the concentration of the borates goes up a little when the water evaporates (i.e. water level drops so less water in the spa), but when you add more water to refill it back up you dilute it back to exactly where it started. I repeat, evaporation and refill do not change the chemical levels of the water for chemicals that are not in fill water (there are no borates in fill water). What may happen is that the CH level may rise with evaporation and refill because fill water usually has some CH (some fill water has a lot of CH).

And yes, the exact borate level is not critical since it's just used for pH buffering. The test strips only show broad ranges. Anything in the 30-70 ppm range should be fine so having the test strip look most like the 50 ppm reference instead of the 30 or 80 one is all you need to do.

[dlleno]

awesome thanks. more dots connected! :-). o good; borates are not volitile. You've confirmed for me that testing for borates isnt critical, and that using the pool calculator (19 oz boric acid for my 500 gal spa) is enough. In fact, if I used the pool calculator correctly, and then used the strips, what would I be testing - the pool calculator or the strips?

BTW, what does the pool calculator mean when it refers to a unit of weight "by volume". For example it says 21 oz "by volume" (of boric acid), which makes no sense. Unless this refers to that volume which, when filled with water, would weigh 21 oz? That is, a convinience for folks who don't have scales and depend on the measures of volume that assume the density of water, i.e. 8 onces per cup?

[chem geek]

You figured it out. You can have ounces that are weight as in 16 ounces in a pound and you can have ounces that are volume as in 8 ounces in a cup. The calculator gives you both since most people don't use a scale to measure their pool chemicals and instead measure by volume which for spas is usually teaspoons or tablespoons, though with borates since the quantity is larger that's in ounces and is more than one cup. The measurement by volume is an approximation since the bulk density can vary, but it's what most people do.

Yes, using the strips would be a double check, but given the wide range it's not that important.

[dlleno]

ok good. So 21 oz "by volume" assuming the density water would be 21/8 = 2.625 cups, so for all practical purposes 2 3/4 cups of boric acid for a 500 gallon spa, which is only 1 ounce (or about 5%) more than prescribed.

I think I'll try that on my next fill!

[chem geek]

Boric Acid bulk density is lower than that of water so use The Pool Calculator for a somewhat more accurate calculation, though just using water density won't be terrible.

[dlleno]

ok I need to rewind a bit here to explain myself better and also to help me understand what appear to be the assumptions used by the pool calculator. I think I need a real chemist to set my sails here...

The numbers, 19oz "by weight" and 21 oz "by volume" came from the pool calculator. In other words, the pool calculator told me that:

1. 19 real ounces (measured on a scale) of a substance that can be purchased today under the label, "Boric acid", is required to achieve 50ppm Borates in a 500 gallon vessel. ok, so Boric acid must be readily available, easy to identify and easy to purchase.

2. 19 real ounces of that same substance would measure as "21 ounces" when placed inside of some volume measurement tool that is labeled in units of weight. Some assumptions have to be made here, which I will get to ...

The process of measuring the weight of any substance "by volume" depends upon the density assumed by the measuring device, and the most natural approach is to assume the density of water. This might sound like captain obvious, but recall for example that one cup is not always 8 ounces. A cup of cooking oil weighs about 6.4 ounces and a cup of table salt weighs something like 9.6 ounces. Interestingly enough, there is a compound known as "Boric Acid" which, in its pure form, would weigh 19.7 ounces per cup!

The casual observer surfing the net will notice that the term "Boric Acid" is applied to more than one compound. For example there is the substance H3BO3 "Hydrogen Borate", which is available from Amazon at approximately $7 per pound. This compound weighs about 11.5 ounces per cup (density greater than water), in its purest molecular form (assuming it is available that way). Apparently, however, we don't put this into our pools and spas, or the pool calculator would have a very different "by volume" conversion factor!

The granular substance commonly available on the market, recommended on this site for the purpose of pH buffering and labeled "Boric acid", appears to be Boric Oxide, B2O3. I came to that conclusion because Duda Diesel does not sell H3BO3; they sell Boric Oxide, B2O3 and label it "Boric Acid". This is a compound which, in its pure molecular form, is 2.46 times heavier than water. However, it is not available in its pure molecular form, it is available as ~56% Boric Oxide with a density that is actually LESS than that of water. hmmm... the plot thickens

This raises two important questions with respect to the pool calculator's recommendation for Borates:

1. Does the pool calculator in fact assume ~56% Boric Oxide B2O3 (as supplied by Duda) to calculate the weight of the substance it calls "boric acid" to achieve the target level of borates? Or does it assume H3BO3 perhaps in some near pure form? I'm not a chemist but it looks to me like either would work: B2O3 has twice as many Boron atoms as does H3BO3 (Boron must be heavy), but at 56% purity, it would contain about the same number of boron atoms as the same volume of H3BO3! but now I'm way over my head and its starting to hurt. Does it matter whether we put H3BO3 in the water or B2O3?

2. If the pool calculator does in fact assume ~56% B203, I'm not following its "by volume" approximation which applies a factor of 1.073 (It says 382 ounces "by weight" required for a 10,000 gallon pool, or 410 ounces "by volume"). where did that conversion factor come from? According to the American Borate company, the density of their 56.3% B2O3 product is approximately 49-51 lbs per cubic foot. Lets call it 50. The density of water is approximately 62.3 lbs per cubic foot (at room temperature), which translates to a "by volume" factor of 1.246, not 1.073, and results in a pool calculator error of about -14%, or about 4 pounds "short" in a 10,000 gallon pool. Something tells me that no one is going measure that much boric oxide using a kitchen measuring cup, so pool owners are likely immune to this error -- they will use true weight, not volume. But for us hot tub owners who dont' own scales...

also: assume for sake of discussion that the pool calculator is not using the density of water in its "by volume" approximation, but perhaps some average or approximation of the density of commonly used dry pool chemicals -- and that the volume measuring devices you obtain from the pool store calibrated in "ounces" are based on that approximation. I don't believe this can be true , as the density of two very common chemicals -- sodium bisulfate and sodium bicarbonate -- have such different densities it would be silly to assign the same approximate density to both. This is why it makes sense - IF you are going to measure weight in terms of volume -- that you use a measuring device that always assumes the density of water -- like ordinary tablespoons, teaspoons and cups, and then apply the appropriate conversion factor based on the actual density of what you are trying to measure.

that is, the "by volume" factor is (density of water)/(density of substance).

So the pool calculator may be on the right track here, but something just doesn't line up re: the "by volume" factor of 1.073. Real 56% Boric Oxide is lighter (less dense) than this: therefore, either the "by volume" conversion factor is just some silly mistake, or it is assuming the wrong density of B2O3 altogether, in which case both numbers are in error.

back to my 500 gallon spa: So I have this 56% Boric Oxide stuff that just arrived from Duda. If I trust the pool calculator's "by weight" calculation of 19 ounces of "Boric Acid", (that it refers to 56% Boric Oxide), then I would want to apply the 1.246 "by volume" conversion factor, not 1.073. (density of water)/density of substance). In other words, I put in 3 cups of B2O3 into the water, instead of 2.75.

calling chem geek....lol

(edited 1/23/2014)

[chem geek]

There is no "density assumed by the measuring device". The volume measurements are absolute. It just turns out that the way they were defined that 1 ounce of volume of water is approximately 1 ounce of weight, though this isn't exactly true and of course water density varies by temperature as well. 1 ounce volume is 29.5735 liters while 1 ounce weight is 28.3405 grams. So having 1 ounce weight being the same as 1 ounce volume implies a density of 28.3405/29.5735 = 0.9583 g/ml. The density of water is not that low even at spa temperatures where it is still 0.992 g/ml, though as a first approximation it isn't terrible (it's a 3.4% error).

When you buy boric acid, you aren't buying a solid crystal. The bulk density of any substance is not an absolute since it depends on the specific granule sizes and also on how tightly it is packed. Even tapping a container against a surface can concentrate the chemicals somewhat if they aren't already that compact. So the use of volume is a convenience, but it isn't as accurate as weighing. The bulk density of boric acid in The Pool Calculator is assumed to be roughly 0.89 g/ml.

Duda Diesel does NOT sell boric oxide. Some data sheets may refer to EQUIVALENT boric oxide content which presumes all water is removed. B(OH)₃ for boric acid becomes B₂O₃ if you heat the boric acid to remove all effective water content so for two boron that would be 6 hydrogen and 3 oxygen removed which would leave 3 oxygen left. The Pool Calculator assumes pure boric acid. 100% boric acid is equivalent to 56.3% boric oxide with the rest water (hydrated chemically to be in boric acid):

B₂O₃ + 3H₂O ---> 2B(OH)₃

Boric Oxide + Water ---> Boric Acid

Boric Oxide .... 69.62 g/mole

3 Water .......... 3*18.01 g/mole = 54.03 g/mole

--------------------------

2 Boric Acid .... 2*61.83 g/mole = 123.66 g/mole

69.62/123.66 = 56.3%

What do you think the extra ingredient in what you assume to be Boric Oxide by Dudadiesel actually is? It's water. Dudadiesel sells boric acid. The fact that they report it in a data sheet as equivalent boric oxide doesn't change the fact that it's really boric acid. The datasheet should list the rest as water, but they often do not when the datasheet is about a chemical that is hydrated since the water content as the "missing" ingredient is presumed.

[dlleno]

ok I'm following you now -- just some semantic and terminology differences remain, I believe, probably because I'm not a chemist. Dimensional analysis and units of measure are important to me and I like to be precise.

If you hand me a US/English measuring cup and tell me that it will measure 8 ounces of something when full, then I will tell you that you (and the measuring device) are assuming the density of water. If I then fill that cup with cooking oil and triumphantly declare that I have measured 8 ounces, I will be wrong because I did not respect the density assumed by the measuring device you gave me, written or implied or stated it doesn't matter. If I go into a convenience store, and select a "32 oz" plastic object shaped like a large cup, with the intention of filling it with Coke, then that volume measuring device is assuming the density of water (a good assumption, to be sure). And if I fill that 32 oz vessel with popcorn I will certainly not have 32 ounces of popcorn because I did not respect the density that the volume measuring device assumed when it declared itself to be "32 oz"

So -- when the pool calculator says "19 ounces by weight equals 21 ounces by volume", that means it has assumed the density that results in that relationship. My job, then, is to understand what that means in terms of my ability to accurately measure the right amount of boric acid.

As for the volume/weight equivalence itself, I see the derivation, and that helps me understand why the pool calculator does what it does, so thank you for that. It sounds like that particular density factor happens to be assumed and accepted within some technical community and that the equivalence has some purpose or practical application somewhere (that I don't see yet because I'm not a chemist). But it doesn't really (accurately) help answer the question at hand, which is: How much (volume) of this white granular substance that just arrived from Duda do I put into my spa? It would seem more prudent to use the bulk density of the substance itself, in the form that I received, and at the temperature which I expect to measure it -- rather than some theoretical density figure that has little correlation or relationship to what I am trying to measure.

I also see the chemistry that you described, which is that the white granular stuff in the bag from Duda really is boric Acid, due to the fact that it is a combination of Boric Oxide and water. Moreover, I now see that the 56% figure is itself affirmation that the substance is in fact pure Boric Acid, and that the substance is stable in that form. If the percentage were any different, then the chemistry you described would not apply, and the substance would not be pure Boric Acid, You are just confirming that when the Pool calculator says to use 19 ounces of pure Boric acid, this means "19 real ounces of that white stuff from Duda that is 56% Boric Oxide by analysis". now it makes sense.

Now back to the volume equivalence. If I am to measure 19 real ounces of the stuff I got from Duda, and I can't measure ounces directly because I don't have a scale, then I have to use a volume measuring device that is calibrated in weight, either physically or in my head. That means the volume measuring device I would expect to use, in order to measure this weight, has to assume the right density. In order for my measurement to be accurate, why would I use the pool calculator's "by volume" approximation? why wouldn't I use the actual bulk density of the stuff I got from Duda?

If I am to use the volume of a U.S /English cup to measure the weight of my boric acid ,I have to calibrate that cup according to the density of my boric acid that I have in my hands (well, in my garage). To do this, I will write "6.33oz" (approximately) at the top of that cup (or in my head). that is, 1 cup of Boric Acid weighs 6.3 ounces. Is that not right? or is the bulk density I saw (50lbs per cubic foot) not the right number to use for this purpose?

Assuming it is the right number, I Now have a volume measuring device that has assumed a particular density and is now calibrated to measure the weight of my boric acid: Three of those cups will equal 19 ounces. FYI I derived that figure from using the advertized bulk density of boric acid supplied as 56% by analysis Boric Oxide. I assumed that this density would itself assume room temperature and so I used the density of water at the same temperature, for the calculation.

The pool calculator is doing the same thing just expressing it differently-- is it attempting to express the real weight "by volume" and it is using the conversion factor that you derived. However, when the pool calculator says that 19 real ounces is 21 ounces "by volume" that means nothing to me because I have no measuring device that is calibrated in ounces which, when filled to the "21 oz" mark, will yield a 19 real ounces of pure boric acid.

If one insists on expressing 19 real ounces of Boric acid in terms of some different number of "ounces" I would rather choose a conversion factor that makes sense and reflects the temperature of the substances of interest when I make the measurement (not spa temperature). So I choose this ratio: (density of water)/density of boric acid) = 1.246. Now I can think of my US/English measuring cup in terms of 8 "ounce" equivalent units, and all I need to do is multiply the real 19 oz by this ratio to find out how many of these "cups" I need. This correlates to something useful: ergo, 19 real ounces is 24 ounces "by volume". equals three cups

Of course I believe your derivation of the volume / weight equivalence. I'm sure it has basis in something useful, just not for this. or am I really into the weeds now?

(edited 2/24/14)

[chem geek]

If you hand me a US/English measuring cup and tell me that it will measure 8 ounces of something when full, then I will tell you that you (and the measuring device) are assuming the density of water. If I then fill that cup with cooking oil and triumphantly declare that I have measured 8 ounces, I will be wrong because I did not respect the density assumed by the measuring device you gave me, written or implied or stated it doesn't matter. If I go into a convenience store, and select a "32 oz" plastic object shaped like a large cup, with the intention of filling it with Coke, then that volume measuring device is assuming the density of water (a good assumption, to be sure). And if I fill that 32 oz vessel with popcorn I will certainly not have 32 ounces of popcorn because I did not respect the density that the volume measuring device assumed when it declared itself to be "32 oz"

You are completely wrong here. There is no assumption about the density of water unless you mix up volume and weight measurements. If someone gives you a cup of cooking oil and declares that they have measured 8 ounces, they are CORRECT if that claim is about volume -- namely, 8 fluid ounces. It is only wrong if they then claim that they have measured 8 ounces WEIGHT. If you fill a 32 ounce vessel with popcorn then you DO have 32 ounces of VOLUME of popcorn (in bulk, which includes the air between kernels). You do not have 32 ounces WEIGHT of popcorn. Remember that "ounces" is used for two different units of measurement -- volume and weight. And as I had indicated, 1 ounce volume of water is NOT 1 ounce weight of water though it is a rough approximation. There are other "ounce" units such as troy ounces where 1 troy ounce is 1.09714286 avoirdupois ounce (avoirdupois is what you have been using for ounces weight).

This is why The Pool Calculator uses the approximate bulk density for the material of interest in calculating the approximate volume from the precise weight. If you want more accuracy in your dosing, then use a scale and dose by weight. Or you can measure the density of your actual product you are using and then use volume calculated from The Pool Calculator weight using your own density number. In practice, the bulk densities assumed in The Pool Calculator are close enough given all the other errors that exist such as actual pool/spa water volume and purity of actual product.

Now back to the volume equivalence. If I am to measure 19 real ounces of the stuff I got from Duda, and I can't measure ounces directly because I don't have a scale, then I have to use a volume measuring device that is calibrated in weight, either physically or in my head. That means the volume measuring device I would expect to use, in order to measure this weight, has to assume the right density. In order for my measurement to be accurate, why would I use the pool calculator's "by volume" approximation? why wouldn't I use the actual bulk density of the stuff I got from Duda?

Again, you are going off on tangents here that make no sense. There is no "calibration" of a volume measuring device to some presumed density or type of substance. The volume is absolute. There is a definition for ounces volume, period. You can then use a density number to convert from ounces weight from The Pool Calculator to ounces volume of the substance you have. The Pool Calculator already does that conversion for you, but assuming a certain bulk density that we got from a combination of published sources and actual measurements of actual product. Yes, it's not exact because product densities can vary somewhat, but for people who don't have a scale or don't want to measure by weight, it's much, much better than simply throwing something in by guessing. So yes, if you could use the actual bulk density of the stuff you got from Dudadiesel, you should do that, but without a scale you can't calculate what that actual bulk density is for your product.

The number 50 pounds per cubic foot is the same density as 0.80 g/ml so is lower in density than the 0.89 g/ml assumed by The Pool Calculator. I measured boric acid I have received from The Chemistry Store and from AAA Chemicals and these measured roughly 0.86 g/ml though it of course depends on how much you tap down the bulk product (i.e. fill a container and tap the container against a hard surface to settle the material). The only way to know the rough bulk density of your actual product is to weigh it and see its volume.

As for calibrating your volume measuring device, forget that. Go the other way around which is far easier. Use the accurate weight from The Pool Calculator to calculate dosages for what you want and then divide that number by the density (in appropriate units) to get to the volume you want. Then use a regular volume measuring device such as measuring cup. I do this all the time when measuring chemicals for my pool. I don't have any "calibrated" volume devices -- I just use the volume that is already calculated (either from my spreadsheet or from The Pool Calculator) and use standard measuring cups.

The pool calculator is doing the same thing just expressing it differently-- is it attempting to express the real weight "by volume" and it is using the conversion factor that you derived. However, when the pool calculator says that 19 real ounces is 21 ounces "by volume" that means nothing to me because I have no measuring device that is calibrated in ounces which, when filled to the "21 oz" mark, will yield a 19 real ounces of pure boric acid.

Again, you are completely wrong here. You do have a measuring device that has ounces volume -- it's called a measuring cup. The 21 ounces volume from The Pool Calculator is absolutely the same 21 ounces of volume in your measuring cup. The only issue is whether the bulk density assumption in The Pool Calculator is close enough to the actual bulk density of the product you have. It's usually close enough. Again, if you want more accuracy, then measure by weight. If you want to normally measure by volume because it's easier, then if you have a scale you can calculate the density of your actual boric acid from Dudadiesel and then use the weight from the Pool Calculator divided by the density you found to get a volume measurement you use with your standard measuring cup. Again, there is no need to "calibrate" your measuring cup -- that's a pain in the behind to do. Just compute the volume you need where that volume is in standard volume units already used by your existing measuring cup.

If one insists on expressing 19 real ounces of Boric acid in terms of some different number of "ounces" I would rather choose a conversion factor that makes sense and reflects the temperature of the substances of interest when I make the measurement (not spa temperature).

The density of your bulk substance will not vary by temperature enough to be measurable by typical household scales and volume measuring devices (such as a measuring cup). The density variation will be almost completely from the settling aspect of the substance or from variations in the granule sizes from different manufacturers. For example, the powdered Boric Acid from Dudadiesel is much less dense than the granular Boric Acid (33-37 pounds per cubic foot for powder vs. 50-60 pounds per cubic foot for granular). The Pool Calculator assumes use of the granular boric acid because that is what most online sources sell and because the powdered form tends to sit on top of the water or clump and not sink to dissolve quickly. Pouring a substance into another container has a loose lower bulk density, but then tapping the container against a hard surface has the substance settle (fills in gaps) and the density will then be higher. Such tapping reaches a rough limit so generally when measuring granular or powdered substances by volume one wants to do such tapping to get somewhat better consistency.

Of course I believe your derivation of the volume / weight equivalence. I'm sure it has basis in something useful, just not for this. or am I really into the weeds now?

You are so far into the weeds as to defy description. It's all a moot point until you get an accurate scale and use accurate volume measuring devices. The entire discussion can be boiled down to "The bulk density assumption used in The Pool Calculator may not reflect the actual bulk density of the product I am buying from Dudadiesel. For greater accuracy, I could measure the bulk density of the actual product I am using or for even more accuracy I could measure the product by weight every time I want to use it."

The 19 ounces weight of boric acid you refer to would be 50 ppm Borates in 500 gallons. The Pool Calculator says this is approximately 21 ounces volume. You found a source claiming a bulk density for boric acid of 50 pounds per cubic foot (which is the same as 0.8355 ounces weight per ounces volume) which would give 23 ounces volume (not 24 that you wrote). If the 50 pounds per cubic foot density were correct and The Pool Calculator were wrong, then using The Pool Calculator would result in 46 ppm Borates instead of 50 ppm. Who cares? This difference doesn't matter and in practice the 50 pounds per cubic foot is probably wrong since every measurement we've made has shown higher density with reasonable tapping to settle the material.

So why don't you buy an accurate scale and perhaps an accurate volume measuring device and calculate the bulk density for your tapped-down product and report back here to us with your results?

[dlleno]

ahh. you sir have identified the problem in your first paragraph, with the rest of the verbiage correct, although unnecessary. I live in a world where an ounce is a unit of weight (ok mass) and when the pool calculator said "ounces by volume" that never once rang the bell, "fluid ounces ,dude!", which of course is a unit of volume. Ounces by volume meant "converting mass to volume using some assumption of density" so: "ounces by volume" = conversion to the well known unit of volume known as the fluid ounce. doh! Had I made that correlation this would all have made sense. Moreover, the painful excursion into the weeds for which I most profusely apologize would not have happened, had I correctly applied those two units of measure. repeat: an ounce is a unit of mass and there are more than 8 of those in a US/English cup. doh! repeat: a fluid ounce is a unit of volume and there are exactly 8 of those in a US/English cup. repeat: somebody made up a new term to me called a "ounce by volume" that really means "fluid ounce"yes even with my misapplication of the units the error was only 10-15 percent of. and by the way I rounded up to 24 oz with the rest of the error caused by the unit mixup ... But in any case it is now clear the the pool calculator is simply converting ounces to fluid ounces.the only confusion that remains is

the powdered Boric Acid from Dudadiesel is much less dense than the granular Boric Acid (33-37 pounds per cubic foot for powder vs. 50-60 pounds per cubic foot for granular). The Pool Calculator assumes use of the granular boric acid because that is what most online sources sell

So Duda sells powdered, they are a minority among on-line sources, and their stuff is like 1.5x bulkier. Since the Pool calculator assumes 55 ish is lbs per cubic foot (as supplied by the American Borate company, for example), this appears to be a significant density difference, no? Therefore, would it not be best to apply an appropriate factor to account for this? I mean if the pool calculator tells me to us 23 fluid ounces of granular, should I not use 30 something ounces of powder? I'm not feeling the urge to purchase scales and weigh this stuff, just the urge to understand the most accurate way to measure the right amount by using a US/English cup.

[chem geek]

So Duda sells powdered, they are a minority among on-line sources, and their stuff is like 1.5x bulkier. Since the Pool calculator assumes 55 ish is lbs per cubic foot (as supplied by the American Borate company, for example), this appears to be a significant density difference, no? Therefore, would it not be best to apply an appropriate factor to account for this? I mean if the pool calculator tells me to us 23 fluid ounces of granular, should I not use 30 something ounces of powder? I'm not feeling the urge to purchase scales and weigh this stuff, just the urge to understand the most accurate way to measure the right amount by using a US/English cup.

Since Dudadiesel sells BOTH granular and powder, there is no reason to have an option for powder in The Pool Calculator since as I wrote it does not work as well since it tends to sit on top of the water and clumps. Since granular is more common and since it is also available from Dudadiesel, assuming granular is reasonable.

[spidey9]

I'm not feeling the urge to purchase scales and weigh this stuff, just the urge to understand the most accurate way to measure the right amount by using a US/English cup.

Why not, since you seemed to be concerned with accuracy? I purchased an inexpensive ($20 or so) digital kitchen scale online and dispense all of my chemicals by weight, thus eliminating any concerns about variations in density.

I can zero the scale after I put the cup on it, which makes weighing out the chemicals a snap. It really doesn't take any longer than measuring by volume.

[dlleno]

ok, so first about powdered Boric acid from Duda. thats a rat hole not worth exploring anymore; Chem Geek when you said " For example, the powdered Boric Acid from Dudadiesel" I thought you were saying that Duda sold ONLY powdered which meant to me that whatever is in the box I just received from them must be powdered. I had to check my order though, and the label: Rest assured I have the granular.

and, convinced now of my error regarding units, I see no reason not to use the pool calculator's assumption of the volume of granular Boric acid, expressed in fluid ounces. but there is a more accurate way...

my interest in accuracy is more about reducing the problem of compounding tolerances -- the calculation will have some small error due to its assumptions of bulk density which themselves have a tolerance. ON top of that you have the error of the volume measuring device itself and one's method of filling it. I have access to a postal scale which I can use to "calibrate" my measuring cup. or better yet measure out portions of 19 ounces -- something I will use only as often as I fill up my spa.