Need Advice On Ph And Chlorine

[TimW]

I am new to the forum and would love some advice. I have had a Nordic Sport (300 gallons) for about 5 years and recently had to replace the pump after the seals kept leaking (which lead to rusty bearings). I had been using softsoak and in talking to the dealer decided to switch to a Nature 2 cartridge along with Spaguard shock and chlorinating concentrate. With this new regiment, I have been having a really hard time keeping the PH from getting too high. Over the past 2 months, I have dumped in almost 2 lbs of sodium bisulfate. The dealer has not been very helpful and his knowledge seems pretty limited. I seem to be able to get it leveled (according to the softsoak test strips which the dealer said will work fine to test the PH even after switching to chlorine), but within a day or so it bounces right back up. The TA has stayed fairly constant at 125. The spa is kept covered, the aerators are off, and my girlfriend and I use it for about 30 minutes at a time about 5 days a week.

I am thinking I need to drain the tub as I am starting to get scared that I am going to kill another pump if I cannot get things under control. If you don't think I need to refill it, any suggestions on getting things under control?

If I should refill it, any advice on getting things under control from the beginning and a simple regimen for keeping them that way?

Also, using chlorine, any suggestions on good test strips to use?

Thanks in advance for your time!

[chem geek]

Tim,

Spaguard chlorinating concentrate is nothing more than the Dichlor form of chlorine that contains BOTH chlorine AND Cyanuric Acid (CYA). You should not use this product exclusively -- use it the first few times and then switch to regular bleach (unscented). The reasons for this may be found in this thread on this forum. SoftSoak is sold as a sanitizer, but is really more of an algae preventative and not as effective as a disinfectant. It is quite acidic which is why you didn't have the pH rise as much before (and is why you needed a high TA of 125 ppm). [EDIT] Actually, the MSDS says that it is not acidic with a pH of 7-8, but the chemical composition looks to me like it would be. [END-EDIT]

The easiest way to lower the amount of rise in pH in your spa is to lower your TA level to around 70 ppm (only to be done when you no longer use an acidic form of chlorine, which is what you will be doing now). I describe how to lower the TA in the link I gave above. The pH rise is due to the outgassing of carbon dioxide from your spa when you aerate your spa each day when you use it. In essence, the spa is "over-carbonated" so it gives off carbon dioxide just like a carbonated soft drink would and this makes the pH rise. As for test strips, waterbear might be able to offer some suggestions for that, but I would get the Taylor K-2006 test kit instead since you will be able to accurately measure your chlorine levels with the FAS-DPD drop test for chlorine in that kit which will also test for pH, TA, CYA, and CH. Since your CYA will be kept very low (20 ppm or lower), you won't be able to test for it readily (the test only starts measuring at 30 ppm, but a cloudy water test even without the black dot disappearing means that some CYA is present at a level near 20 ppm).

If you refill the spa, then you start out by adding calcium chloride to raise CH (to 200 ppm -- but if your spa heater has corrosion resistent cupro-zinc [EDIT] I meant cupro-nickel [END-EDIT] in the heat exchanger and you have no exposed grout/plaster touching spa water, then you may not need to add calcium higher than is what already is in your fill water) and Baking Soda (sodium bicarbonate) to raise the TA (to 70 ppm) and some acid (sodium bisulfate) to lower the pH (to 7.5) and of course some Dichlor for chlorine (to 4-8 ppm FC). Then after that, just add some Dichlor (the first few times -- not more than the equivalent of 20 ppm Free Chlorine amount cumulative) or bleach after each use. Check the FC level before you get into the spa to make sure it is high enough (after you've switched from Dichlor to bleach, the FC level should be at least 4 ppm -- not more than 8 ppm) and test the Combined Chlorine (CC) level to see that it is less than 0.5 ppm (if not, then you need to add chlorine (bleach) to shock with 10x the amount of chlorine as the CC level -- this should happen infrequently if you maintain your FC level consistently).

You do not need to use the Nature 2 system (which is just metal ions such as copper and/or silver) if you maintain proper chlorine levels and keep your CYA low (which you do by only using Dichlor a little and then switch to using bleach).

[TimW]

Chem Geek,

Thanks for all the info! I have not taken a chemistry class in 25+ years, but I think I follow. I am going to drain the tub this weekend and follow your instructions. A couple of questions about them.

After adding each chemical, how long do I need to wait before testing?

Will the Taylor K-2006 test kit give me a guide of about how much of each chemical to add in order to reach the desired ppm?

I find that adding chemicals after each use is a hassle as it means I need to leave the cover off and run the jets for 20 minutes. As I often soak before bed this is a nuisance. Is it reasonable to only add dichlor or bleach weekly if there are only two people using the tub?

Once I follow your initial instructions:

If you refill the spa, then you start out by adding calcium chloride to raise CH (to 200 ppm -- but if your spa heater has corrosion resistent cupro-zinc in the heat exchanger and you have no exposed grout/plaster touching spa water, then you may not need to add calcium higher than is what already is in your fill water) and Baking Soda (sodium bicarbonate) to raise the TA (to 70 ppm) and some acid (sodium bisulfate) to lower the pH (to 7.5) and of course some Dichlor for chlorine (to 4-8 ppm FC).

and get all the levels set, how often should I be testing it?

Thanks again for your time and advice.

Best,

Tim

Tim,

Spaguard chlorinating concentrate is nothing more than the Dichlor form of chlorine that contains BOTH chlorine AND Cyanuric Acid (CYA). You should not use this product exclusively -- use it the first few times and then switch to regular bleach (unscented). The reasons for this may be found in this thread on this forum. SoftSoak is sold as a sanitizer, but is really more of an algae preventative and not as effective as a disinfectant. It is quite acidic which is why you didn't have the pH rise as much before (and is why you needed a high TA of 125 ppm).

The easiest way to lower the amount of rise in pH in your spa is to lower your TA level to around 70 ppm (only to be done when you no longer use an acidic form of chlorine, which is what you will be doing now). I describe how to lower the TA in the link I gave above. The pH rise is due to the outgassing of carbon dioxide from your spa when you aerate your spa each day when you use it. In essence, the spa is "over-carbonated" so it gives off carbon dioxide just like a carbonated soft drink would and this makes the pH rise. As for test strips, waterbear might be able to offer some suggestions for that, but I would get the Taylor K-2006 test kit instead since you will be able to accurately measure your chlorine levels with the FAS-DPD drop test for chlorine in that kit which will also test for pH, TA, CYA, and CH. Since your CYA will be kept very low (20 ppm or lower), you won't be able to test for it readily (the test only starts measuring at 30 ppm, but a cloudy water test even without the black dot disappearing means that some CYA is present at a level near 20 ppm).

If you refill the spa, then you start out by adding calcium chloride to raise CH (to 200 ppm -- but if your spa heater has corrosion resistent cupro-zinc in the heat exchanger and you have no exposed grout/plaster touching spa water, then you may not need to add calcium higher than is what already is in your fill water) and Baking Soda (sodium bicarbonate) to raise the TA (to 70 ppm) and some acid (sodium bisulfate) to lower the pH (to 7.5) and of course some Dichlor for chlorine (to 4-8 ppm FC). Then after that, just add some Dichlor (the first few times -- not more than the equivalent of 20 ppm Free Chlorine amount cumulative) or bleach after each use. Check the FC level before you get into the spa to make sure it is high enough (after you've switched from Dichlor to bleach, the FC level should be at least 4 ppm -- not more than 8 ppm) and test the Combined Chlorine (CC) level to see that it is less than 0.5 ppm (if not, then you need to add chlorine (bleach) to shock with 10x the amount of chlorine as the CC level -- this should happen infrequently if you maintain your FC level consistently).

You do not need to use the Nature 2 system (which is just metal ions such as copper and/or silver) if you maintain proper chlorine levels and keep your CYA low (which you do by only using Dichlor a little and then switch to using bleach).

[chem geek]

Tim,

If you have some jets running or other form of circulation, you can test the water after just a few minutes (say, 5 minutes). In a large pool with the pump running, most easy-to-mix chemicals such as chlorine are dispersed rather well in 15 minutes and after 30 minutes are pretty much thoroughly mixed, so in a spa I would expect this to be much, much faster due to the much smaller water volume. pH changes tend to take a little longer to stabilize, but again in your spa it shouldn't take very long.

As for how much to add, I can roughly calculate that for you, at least for some chemicals, given your spa's 300 gallon volume. If your fill water (that you can test directly) already has some Calcium Hardness (CH) to it, and if you have no plaster/gunite/grout surfaces (including tile with grout) and if your heater is corrosion resistant, then you probably do not need to add any extra calcium. If you do, then it would take 8.8 ounces (weight) or about 4 fluid ounces (8 tablespoons) of anhydrous calcium chloride or 10.3 ounces (weight) or 12 fluid ounces (24 tablespoons) of calcium chloride dihydrate to add 200 ppm, but you need to reduce this proportionately based on how much CH you already have (so if you already have 50 ppm, then you add 150 ppm which would be 150/200 of the amounts I gave you).

To add 70 ppm to TA, you would add 4.75 ounces (weight) or about 2 fluid ounces (4 tablespoons) of baking soda (sodium bicarbonate), but again this assumes you are starting from 0 ppm TA so scale down accordingly depending on the TA of your fill water.

You will probably need to add a little acid to bring down your pH. If after the above your pH is 7.8, then to get to 7.5 you need to add 0.24 ounces (weight) of sodium bisulfate acid or 0.092 fluid ounces (about half a teaspoon). However, since I have no idea what your starting pH, TA and CH will be, I can't tell you what you will need to do for pH, but this example should give you a rough idea.

For chlorine, adding 4 ppm FC takes 0.29 ounces (weight) of Dichlor. I don't know the density of your Dichlor product but the MSDS says it is 56-60 pounds per cubic foot which is about 0.97 ounces (weight) per fluid ounce (seems a little low to me as that is the density of water) so this is about 1.7 (one and two-thirds) teaspoons. After you switch to bleach, it takes 2.5 fluid ounces (5 tablespoons) of 6% bleach for this same 4 ppm FC.

As for frequency of addition, that is something you will have to see for yourself by measuring chlorine levels. You can add the chlorine before you get into the spa and adjust other chemicals that way as well. You don't have to adjust afterwards. Just make sure that each time you go in you have enough chlorine. You'll have to see how much chlorine loss there is each day and you can maintain a higher level to account for this loss -- so start at 8 ppm FC and then add more when it gets to 4 ppm FC, for example. Once you get used to your spa's chemical pattern, you won't have to add chemicals as often, but I doubt that you'll be able to maintain your chlorine over a week. Sweating in such a small volume of water will use up chlorine rather quickly.

As for how often to test, that really depends on how quickly your spa's chemistry changes, so just like the chemical additions above, you'll have to get a feel for that over time. Initially, test each time you get into the spa -- at least test the chlorine level. The pH is the next thing that is most variable so test that as well, especially since you've had such pH swings in the past. The TA level won't change very fast and the CH will change the least as will the CYA so really it's just about testing chlorine and pH levels. I can't say how frequently you'll have to do this, but initially test every day, get a feel for the rates of change, then test less as you feel more comforable. Hopefully you will get to a point where a fairly regular and constant addition of some chlorine and a little acid will be what is needed.

By the way, you said you added about 2 pounds of sodium bisulfate over 2 months so that would be about half an ounce (weight) per day. This would roughly correspond to the amount of acid needed (at 125 ppm TA) to go from a pH of 7.9 to 7.5 so that sounds about right if you were fighting a strong pH rise. Hopefully, the lower TA of 70 ppm will cut down this rise, though it won't eliminate it.