Very Low Ta

[Croc Dundee]

Hi all,

I'm sure this has been covered before somewhere, but what happens when you get a very low TA reading??

The reason i ask is that a couple of weeks ago I has a very low TA of about 40 (PH was about 7.6) I added quite a bit of PH up and got the TA to around 90 (PH rose to about 7.9).

Its now sitting around 80 and my PH is still about 7.9

I've read the threads about the whole TA/PH "catch-22" (so-to-speak) but was curious as to whether having a low TA is the lesser of two evils (ie PH more important) and if so, how low is 'dangerously' low and what will this cause.

Cheers.

By the way my spa is a 2400L (640 gallon - yes its pretty big), 37C (98F), ozonated, Nature2 and I also use Lithium Hypochlorite (about 2Tb / day after soaking)

[chem geek]

Since you do not use an acidic source of chlorine, having a low TA is not a problem and in fact will help prevent the pH from rising as it would normally do from aeration. I probably wouldn't go below 60, however, just to be on the safe side, though with your larger spa perhaps 50 is OK. To raise the TA more than the pH, you would add Arm & Hammer Baking Soda (or Alkalinity Up) instead of pH Up, but there's no problem with using pH Up as some acid will get you back closer to a pH of 7.6 yet won't lower the TA as low as it was (because pH Up is technically a combination of a base that raises mostly pH and baking soda that raises mostly TA). If you added enough pH Up to go from a TA of 40 to 90, that would be around 4.5 ounces weight (about 4 ounces volume) and would raise the pH from 7.6 to 9.4 so something doesn't sound right. It makes more sense that you added Alkalinity Up (Baking Soda) since 7.4 ounces weight (5.9 ounces volume) would raise the TA from 40 to 90 and the pH from 7.6 to 7.8. The extra rise in pH probably came from outgassing of carbon dioxide.

Note that if your spa was plaster/gunite or had tile with exposed grout that you might need to increase the Calcium Hardness (CH) to compensate for the lower TA. For example, you'd have good balance if your pH was 7.7, TA was 50 (CYA was 20), CH was 150. If the spa is fiberglass, then don't worry about the calcium unless you experience foaming in which case raising it to 100 ppm can help.

Did you first use any Dichlor during your first week or so after a fresh refill? If not, then your use of Lithium Hypochlorite will be too strong in chlorine because there won't be any Cyanuric Acid (CYA) in the water to moderate the chlorine strength. You'll get more life out of your cover if you make sure there is some CYA in the water. If you use Dichlor for about a week at around 4 ppm FC per day then that should get your CYA to around 25 ppm which is fine.

If my calculations are correct, I think that 2 tablespoons of Lithium Hypochlorite in 640 gallons is around 4.1 ppm FC which is probably enough for around 1 person-hour of soaking (for example, 2 people soaking for 30 minutes). Does that sound about right? Do you measure any Free Chlorine (FC) residual before you get in? Have you found that the Lithium Hypochlorite dissolves quickly? Some people find that it dissolves slowly, even when pre-mixing in a bucket of water.

Richard

[Croc Dundee]

Thanks for that Richard,

It was definitley PH up that I added - but the readings were taken about 4 days apart and I did add some acid in the meantime so maybe this caused the drop in PH?? (or my readings were askew)

We (two of us) generally soak for around 20-30 mins per night and I have tested the FC before getting in and its usually quite low (<1) but the fact that I have ozone and Nature2 I was under the impression that this was about right??

I find the Lithium Hypochlorite dissolves pretty well... After use I dose with 2 Tb (straight in the spa), I leave two of the pumps running for half an hour (they cut-off automatically) with the air turned off and let the 24hr circ pump do the rest.

Only problem is that it's quite expensive, but hey, we didn't buy the spa to save money!!

I've only ever used the Lithium Hypo, not even sure you can get Dichlor in Australia (??) and to be honest I'm not really sure what it is??

Only had my spa about 6 weeks so still running on the first fill - YES I'm a novice!!

Thanks to this forum and contributers such as yourself, I have learnt a lot in a small time (still lots to learn though)

Cheers

By the way - This is the first day under about 33C in about 3 months In my part of the world (Perth, Western Australia) so can't wait to finally have a soak to 'warm-up' rather than just to go from heat to heat (if you know what I mean?!)

[chem geek]

Yes, if you added acid after adding the pH Up, then that could explain the numbers since the combination of pH Up and acid is technically similar to just adding Baking Soda (or Alkalinity Up) instead of pH Up.

As long as you've got some residual of chlorine, I think you're fine with Nature2 and the ozonator. If you find that you add chlorine and it quickly goes away, then you may be building up ammonia/urea (but I think you're OK based on calculations below). I would think that the ozonator would take care of it, but there's been conflicting reports about that on this forum.

I am positive that you can get Dichlor in Australia. It's often sold as "chlorinating granules" for spa use and you want to look on the label for something that says "dichloro-s-triazinetrione (dihydrate)" or possibly "1,3-dichloro-1,3,5-triazinane-2,4,6-trione (dihydrate)". It's a fast dissolving powder or granules and may say something like Spa 56 since it's roughly 56% available chlorine.

As for the Lithium Hypochlorite, if the expense is too much for you, then you can use Clorox Regular unscented bleach instead (assuming that is sold in Australia). Given the mixed results some have had with bleach, you want to be careful to use a quality bleach -- if it says 6% Sodium Hypochlorite in the ingredients, then that would be good (or even 5.25%). You should always add chemicals very slowly over a return flow with the pump running. But be sure to add some Dichlor as soon as you can -- you are currently over-chlorinating your spa. The CYA in Dichlor will help moderate the disinfecting (and oxidizing) chlorine level.

To get 4 ppm FC in 350 gallons, one would use 2 teaspoons of Dichlor dihydrate or 3 fluid ounces of 6% bleach or 1 tablespoon (3 teaspoons) of Lithium Hypochlorite. Your 2 tablespoons of Lithium Hypochlorite would raise the Free Chlorine (FC) by about 8 ppm in 350 gallons and is about right for one person-hour of soaking, so two people for 30 minutes.

[Croc Dundee]

Ok, I've done a bit of online research and i think I have spotted both the Dichlor and the bleach but under slightly different names and strengths.

1 - Spa Protector (Bleach?) A$33 for 5 litres

Here's the spiel:

"No chlorine or bromine. Hydrogen Peroxide based sanitizer with a content of 190 grams per litre giving it a 19% strength.

Spa Protector oxidizes the bacteria and organic materials, plus dissolves inorganic compounds, leaving the water completely clear & odour free."

2 - Stabilised Chlorine (Dichlor?) $A40 for 4kg

"Sodium based chlorine for sanitising pool water. This product also has stabilizer 'built in' to stop the sun from eating your chlorine. 630 gm/kg. Available chlorine present as Sodium Dychloroisocyanurate."

I like the idea of the dichlor as it has the stabiliser and my wife quite often leaves the cover off in the daylight hours while she's sunbaking.

A question though regading your statement; "But be sure to add some Dichlor as soon as you can -- you are currently over-chlorinating your spa. The CYA in Dichlor will help moderate the disinfecting (and oxidizing) chlorine level."

What exactly do you mean by "overchlorinating"..

Cheers

[chem geek]

The second one is indeed Dichlor, but the first one is not bleach. It's hydrogen peroxide. Just look for standard unscented laundry bleach at your grocery store, but try and find the highest quality brand and preferably one that lists the concentration of Sodium Hypochlorite on the bottle.

Cyanuric Acid (CYA) protects chlorine from degradation from the UV rays in sunlight through two different mechanisms. One is by absorbing UV rays itself so this shields chlorine at lower depths. The other is through combining with chlorine to form compounds that are not effective sanitizers nor oxidizers. Over 95% of the chlorine is in these compounds and less than 5% is unbound to such compounds and only half of that is the strong disinfecting chlorine. So when using CYA, say at 4 ppm FC with 20 ppm CYA, this is equivalent in disinfecting chlorine to having 0.2 ppm with no CYA. So if you soak with even 1 ppm FC being measured, you are exposing yourself to 5 times as much chlorine as is needed for disinfection and this can lead to flakier skin and faster degradation of swimsuits and spa covers and corrosion of metal (though that's still slow).

Richard

[fdegree]

Sorry if I missed the answer to this, but Croc Dundee asked "curious as to whether having a low TA is the lesser of two evils (ie PH more important) and if so, how low is 'dangerously' low and what will this cause." and I'm quite curious as to the answer.

My hot tub tends to run a high pH (7.6 - 7.9) with a low alkalinity (30 - 50). In fact, I just checked it:

pH = 7.8

alk = 40

bromine = 6.0

gallons = 480

Thanks

[chem geek]

Sorry if I missed the answer to this, but Croc Dundee asked "curious as to whether having a low TA is the lesser of two evils (ie PH more important) and if so, how low is 'dangerously' low and what will this cause." and I'm quite curious as to the answer.

My hot tub tends to run a high pH (7.6 - 7.9) with a low alkalinity (30 - 50). In fact, I just checked it:

pH = 7.8

alk = 40

bromine = 6.0

gallons = 480

Thanks

Sorry that I didn't really answer that. Unfortunately, the answer depends on the situation. There are only two reasons one needs a higher Total Alkalinity (TA). One is when there are large changes in pH due to chemical additions or other sources, especially a drop in pH due to acidic sources of sanitation (including accounting for the acidity of chlorine when it gets used up, regardless of the pH of the initial addition). Usually, it's the use of Trichlor tabs in pools that require higher TA for this reason. The other reason one needs a higher TA is to saturate the water with calcium carbonate when the water touches plaster/gunite/grout, but one can alternatively use a higher Calcium Hardness (CH) or pH target to compensate for lower TA.

The only real reason to lower TA is to reduce the rate of outgassing of carbon dioxide which makes the pH rise. In your situation, it's not clear if that is what is happening. If you can turn off all aeration sources in the spa including jets and ozonator and see if that makes any difference in the tendency of the pH to be higher, then that's what is going on. Though technically lowering the TA even lower would reduce the pH rise, I think you'd be getting into too risky territory of not having enough of a pH buffer which is part of what TA does. I generally don't recommend going below 50 for that reason. You don't want to accidentally have the pH drop really low due to some acidic chemical or process.

[EDIT] When the TA is really high and other parameters such as CH and pH are not low, then one can have scaling so that's another reason to lower the TA -- kind of the opposite situation of protecting plaster by saturating the water with calcium carbonate. [END-EDIT]

IF you determine that aeration is causing the pH to rise, then you could add borates (from a combination of 20 Mule Team Borax and acid) as an alternative pH buffer and then have the TA be lower (to lower the carbonates), but that's normally done in some SWG pools and at much higher TA levels than your spa.

I'd say you first need to figure out the source of your rising pH. What chemicals are you adding to get to your bromine level? Are you using bromine tabs and if so what kind? Are you using MPS or something else to shock and if so how often?

Richard

[fdegree]

I'd say you first need to figure out the source of your rising pH. What chemicals are you adding to get to your bromine level? Are you using bromine tabs and if so what kind? Are you using MPS or something else to shock and if so how often?

Richard

I'm still very new to all of this so I'm not sure if my answers will be thorough enough, but I'll try.

I doubt it is aeration, unfortunately our schedules do not allow for much spa usage...maybe 1 time every 10 days (2 adults for about 45 minutes each). When we do get in, we rarely use the the jet pumps, usually just sit and soak in the warm water. So, the only aeration is from the ozone, which runs 24/7, and the once a day "purge" cylce that runs the jet pumps for about 30 seconds (I keep the aeration knobs closed so this "purge" cycle is just water circulation).

For bromine I use the Leisure Time Brom Tabs in a floater that is nearly completely closed.

The Brom Tabs ingredients are:

1-bromo-3chloro-5, 5-dimethylhydantoin..........60.0%

1,3-dichloro-5, 5-dimethylhydantoin.................27.4%

1,3-dichloro-5ethyl-5-methylhydantoin.............10.6%

Other Ingredients...........................................2.0%

Available Bromine...39.2% Available Chlorine...44.4%

I shock with plain laundry bleach...6.0%. About once a month.

My fill water has a pH of something less than 7.0...it is slightly more yellow than the 7.0 on the taylor test kit.

At fill up I add a metal sequesterant (I have iron in my fill water), sodium bromide for the bromine bank, calcium and baking soda. After that initial balancing of the chemicals, I usually only add baking soda about once a month and keep the floater filled with Brom Tabs.

I have noticed when I add the baking soda to raise the alkalinity it also raises the pH. If my memory is working properly, when I add enough baking soda to raise the alkalinity to around 60 - 70, the pH tends to run about 7.8 - 8.0. I have also noticed that, on the rare occasion we have the time to use the spa more frequently, the pH and bromine levels drop. So, maybe the problem is simply not enough usage :-)

It is actually a rather simple process and I am pleased with everything...just wondering about the cautions of low alkalinity.

Thanks, Richard...your help is greatly appreciated.

[chem geek]

I don't see anything that would tend to have the pH rise, but then by not using the tub very much and the bromine tab floater nearly closed then things should be relatively stable. I would say just keep the TA at least at 50, but if you don't notice much difference with it a little higher but not more than 80 then that's fine. This is more for safety than anything else. It doesn't sound like the pH is rising that quickly as you aren't always having to add acid every day or anything like that. Your risk of having the TA even lower than 50 was low since the chemical addition and usage of the spa are very low.

[fdegree]

I don't see anything that would tend to have the pH rise, but then by not using the tub very much and the bromine tab floater nearly closed then things should be relatively stable. I would say just keep the TA at least at 50, but if you don't notice much difference with it a little higher but not more than 80 then that's fine. This is more for safety than anything else. It doesn't sound like the pH is rising that quickly as you aren't always having to add acid every day or anything like that. Your risk of having the TA even lower than 50 was low since the chemical addition and usage of the spa are very low.

I appologize, I didn't explain my situation clearly enough. The pH does not tend to rise for no reason...once things are in tune it does stay rather stable. What happens is the pH rises too high when the TA is increased to a "normal" range. Having a low TA seems to keep the pH in "normal" range. Therefore, I let the TA stay rather low...usually 40 - 60. When it hits 30 I add baking soda to bring it back up to around 60, which causes the pH to run around 7.8 - 8.0. Over time, as the TA drops, so does the pH. So, this is how I have been doing things for the past few months in order to keep from adding too many chemicals.

If I understand this correctly, since I have a Sundance spa with a vinylester, polyester and acrylic layered shell, the calcium levels are not important (except to reduce foaming), and the low TA is not going to harm anything. The only real concern, regarding a low TA, is the increased potential for a large swing in pH. This swing in pH only seems to happen with more frequent usage. At that time I will have to be more diligent with pH and TA control. Please correct me if I am wrong with any of this.

Now for the next logical questions, which have probably been discussed before:

1. What are the ramifications regarding low pH? At what level should I begin to worry?

2. What are the ramifications regarding high pH? At what level should I begin to worry?

Thanks again Richard!!!

[chem geek]

Yes, you've got it regarding the role of TA and your situation in a non-plaster/grout spa.

OK now I get your real question. Sorry it took me so long to get it. Your situation is fine to have the TA be on the low side so targeting the range of 40-60 that you have been doing, but the problem you have is that adding Baking Soda to increase the TA causes the pH to rise. The solution to that is simple and is to just add acid when that occurs to lower the pH. Now it's true that adding acid also lowers the TA some, but not as much as the baking soda increases it. So what you'd really like to know is how much baking soda and acid in combination (one after the other after waiting for mixing between additions) would give you both the TA and pH that you want.

Unfortunately, to get that answer requires complicated computations that are found in my PoolEquations spreadsheet, but I'll give you an idea of it using your data. Let's say that we start with a pH of 7.5 and a TA of 40 and want to know how much baking soda and acid are needed to end up with a pH of 7.5 and a TA of 60. In 480 gallons it takes 2.25 ounces weight (1.8 ounces volume or about 3-1/2 tablespoons or 11 teaspoons) of Baking Soda (or Alkalinity Up) and 0.1 ounce weight (0.07 ounce volume or half a teaspoon) of Dry Acid (sodium bisulfate). Interestingly, I don't find that the Baking Soda raises the pH by very much -- it does raise it, but unless you add a lot it's not by much. From 30 to 60 TA the baking soda should only raise the pH from 7.5 to 7.6.

It's also interesting that over time the pH and TA both drop. That definitely means you've got some acidity in your system, possibly from the bromine tabs and specifically bromine usage (which is acidic, just as chlorine usage is acidic so the bromine tabs themselves are probably similar to Dichlor in being roughly pH neutral upon addition of chemical, but then usage of bromine is acidic). If you raised your target TA level a bit, then you may find that the pH is more stable during the more frequent usage, but it's up to you which of these situations you want to have more stable pH.

As for low pH, you should avoid going below 7.0 for extended periods of time, but realistically you want to be above 7.2 if you can and usually that isn't a problem. As for high pH, it depends on other factors such as TA and CH since the main issue there is scaling. Usually if you stay below 8.0 you are fine, but this again depends on these other factors. It's best to try and stay below 7.8 so a good range is 7.2 to 7.8 though you usually just target something in between depending on which way the pH tends to go over time.

Richard

[fdegree]

As for low pH, you should avoid going below 7.0 for extended periods of time, but realistically you want to be above 7.2 if you can and usually that isn't a problem. As for high pH, it depends on other factors such as TA and CH since the main issue there is scaling. Usually if you stay below 8.0 you are fine, but this again depends on these other factors. It's best to try and stay below 7.8 so a good range is 7.2 to 7.8 though you usually just target something in between depending on which way the pH tends to go over time.

Richard

Thanks Richard, as usual your input is invaluable.

As for pH levels, keeping the pH above 7.0 - 7.2 is never a problem. In fact, I have a box of Borax that I have never opened.

So, scaling is the only issue when the pH runs high, and the chances of scaling also depends upon the TA and CH levles. I'm assuming low CH levels would reduce the likelyhood of this scaling. If I'm correct, then it would by wise if I didn't add any calcium to the fill. Especially, since it's only advantage (in my situation) seems to be reduced foaming, and we don't use any aeration when we are in the tub so we rarely have foaming anyway. Please correct me if I'm thinking backwards on this.

So, what about the TA...would a low TA increase or decrease the chances of scaling when the pH is high?

Sorry if we are rehashing things that you have discussed 100's of times already.

[chem geek]

You've got it exactly right again. Keep the CH low to minimize the risk of scaling since it's only benefit in a non-plaster situation is to reduce foaming and that's not a problem you've got. I think it is still important to keep the pH below 8.0 and ideally below 7.8 most of the time. As for scaling and TA, lower TA has lower risk of scaling because it means there are fewer carbonates in the water (all else equal -- i.e. at comparable pH). However, if your CH were low at 50, then even with a TA of 80 you're not likely to risk scale in the gas heater until at least a pH of 7.9 or higher. With a TA of 50, that risk doesn't start until the pH hits 8.2 or higher. You can use The Pool Calculator to calculate the CSI and if it's at -0.2 or lower (more negative) then that's below the scaling point at the gas heater, roughly speaking. Don't forget to include the temperature of the spa (104F, usually) as the index is temperature sensitive. Don't forget that errors in measurements can easily make such "accurate" calculations not so accurate.

Richard