Very Low Ph

[yitbos1]

First off, this is my first post, so if I forget something or sound like I don't know what I'm doing, I apologize...

My pool (in-ground, vinyl, ~12,000 gal.) currently has very low pH (< 6.8) and cloudy water. I am currently aerating with both returns pointed upward. Actually, for whatever reason, the previous owners had made a few 90 degree angles from PVC that thread into the returns. These I used to make the returns face up above the pool surface, hence a fountain-like effect.

Here are my numbers:

FC - < 0.5 (it was steady at about 2, but then started dropping recently. Separate issue?)

TC - 1ish

pH - < 6.8

TA - 120

CH - 100

CYA - 0

Aeration has been going on for several days without much effect. Do I need to add soda ash to counteract the pH a bit first to get it to a more manageable level or just keep aerating? As for the chlorine, I use an automatic chlorinator with 3" dichlor pucks. I know this isn't ideal, but I am still trying to get my pH in line before I worry too much about the chlorinator.

[chem geek]

Since you don't know how low the pH really is, I would add some 20 Mule Team Borax to get the pH up right away since low pH is the worst thing for vinyl -- you could add 2 76-ounce boxes safely as worst case that would raise the pH from 6.8 to 7.5 so you won't overshoot. It won't raise the TA as much as pH Up product would. However, some things don't make any sense from what you posted (as a first post, the information you provided is excellent so don't worry) -- specifically, I think you mean you use 3" Trichlor pucks (Dichlor is powder or granular) and if you've been using such pucks for a while then you shouldn't have zero CYA. Are these measurements from your own Taylor K-2006 test kit or the TF100 test kit from tftestkits.com? Or are they from a pool store. If from the latter, you should get your own good test kit either here or here with the latter kit having 36% more volume of reagents so comparably priced "per test".

Trichlor is very acidic and it will increase CYA over time. It's fine to use for a while if your CYA is lower and your trying to raise it, but it requires regular addition of pH Up or Borax to maintain the pH. For every 10 ppm Free Chlorine (FC) added by Trichlor tabs/pucks, they also increase Cyanuric Acid (CYA) by 6 ppm.

You may need to supplement the chlorine by using chlorinating liquid or unscented bleach (6% Clorox Regular or off-brand Ultra). However, until we know the true CYA level it's hard to know what to do next. If it's truly near zero, then you'll want to add some CYA since too low CYA will have the chlorine break down from sunlight too quickly. If the CYA is actually high, then a partial drain/refill will be needed to lower it. Sometimes pool stores will measure CYA backwards, incorrectly subtracting the actual reading from 100 because the tube test measures a lower reading the more you fill the tube (and that confuses some people).

Richard

[yitbos1]

Thanks, Richard, for your reply. You seem to be the resident expert and I was hoping you would post.

I actually just bought a Taylor K-2006 since I determined the reagents in the kit from the previous owner were shot. The numbers I gave were partially from that kit and partially from a Leslie's analysis earlier the same day. The CH and CYA numbers are from the latter, so they may very well be off. I will do my own CYA test this evening.

Thank you so much for your info. I will post the CYA as soon as I get it.

[yitbos1]

Tested my CYA and, sure enough, it was not at/near 0 but very high. I would have to estimate 200-300 as the level (using the Taylor K-2006) only got to about halfway to the 100 line. Looks like I am draining and refilling this weekend!

[chem geek]

Tested my CYA and, sure enough, it was not at/near 0 but very high. I would have to estimate 200-300 as the level (using the Taylor K-2006) only got to about halfway to the 100 line. Looks like I am draining and refilling this weekend!

I want to reiterate this point for everyone on this forum to hear. When you took your water sample to Leslie's for testing, they said you had ZERO CYA whereas your own Taylor K-2006 testing showed the CYA level to be extremely high (200+ ppm). This is not an uncommon occurrence since some pool stores seem to "invert" the CYA reading because they get confused that adding more liquid in the test results in a lower number (so some subtract their reading from 100, which is completely wrong). Either that, or their CYA test reagents are bad or their measuring device is not functioning. This is why it is SO important for one to get their own good test kit. They are really easy to use and you can trust the results. Since the CYA level is such an important number to determine accurately (as is FC), you can't always rely on pool stores to do that correctly.

Just so you know all of your alternatives, a drain/refill is the only way to lower the CYA level, but it's not the only way to prevent algae. You could have your high CYA level, but would need to treat algae through one of several methods, each with their own pros/cons. One method is to have a higher FC level which would need to be somewhere around 20 ppm or so -- probably impractical. Another method is to use a supplemental weekly algaecide such as PolyQuat 60, though even then you'll still need chlorine and an FC level of somewhere between 5 and 10 ppm. Another method is to use a phosphate remover in which case the FC level won't have to be very high -- 3 ppm or so would work though for better sanitation 5 ppm FC would be a bit better. Finally, there are other algaecides with side effects such as copper-based algaecides, but that can stain if the pH goes up.

Now that you know how the CYA level got so high -- from continued use of Trichlor and Dichlor stabilized chlorine products -- you can watch that more carefully and possibly use more chlorinating liquid or unscented bleach or even some Cal-Hypo now and then though with the latter you need to watch your CH levels that would increase from Cal-Hypo. Remember the following rules:

For every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm.

For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.

For every 10 ppm FC added by Cal-Hypo, it also increases CH by 7 ppm.

You might consider using The Liquidator talked about in this thread to automate chlorine dosing. [EDIT] Another alternative is to get a saltwater chlorine generation (SWG) system. That has some potential issues with the higher salt levels, but those can be mitigated unless you've already got some soft limestone you don't want to seal. [END-EDIT]

Richard

[yitbos1]

Thanks for the info, Richard. Without you I'd be scratching my head trying to figure out what the problem is.

[yitbos1]

Well, I finally got around to partially draining the pool a couple of times. Let me just say that a 2" outlet submersible pump makes quick work of the job. I neglected the pool until that point so it was quite green and had debris falling in it thanks to a strategically placed honey locust tree. I now despise honey locust trees...

Anyway, after the job, CYA levels were actually very low. I could still clearly see the dot at the bottom of the tube using the K-2006 kit. I wanted to super-shock the water, so I killed two birds with one stone by using dichlor to shock rather than an unstabilized chlorine. After the sun went behind the trees, I added enough to give me 30 ppm. The next morning, FC was back to near zero and CC was about 3, so I super-shocked to 30 ppm again since the morning was overcast. This afternoon, I checked to see where my CYA was, and it is now about 50. I still had about 3 ppm FC and maybe 1-2 ppm CC, but my pH is now very low. It was 7.6 before I started shocking, but now it's off the scale low. Using the base demand test, I needed to add somewhere around 20 drops to get a change in color. Are my chlorine levels mucking with the test or is my pH really that low? I used dichlor (9 lbs total in a 10,000 gal pool), so I didn't think it would affect my pH that much.

At any rate, I just added 3 lbs Borax. I didn't really think things through before doing so, but I was in a bad mood to begin with. I just wanted to do something. Did I do the wrong thing?

Other numbers for reference: TA - 80, CH - 80

[chem geek]

It's OK, don't panic. Dichlor is actually acidic when accounting for both its addition (which is close to pH neutral) and the eventual consumption (usage) of that chlorine (which is acidic). If you started with a pH of 7.6 and a TA of 80, then the amount of Dichlor to raise the FC by 30 ppm (and CYA by 27 ppm) would, after the 30 ppm FC gets used up, result in a pH of 6.9. So this isn't anything unusual.

However, 9 pounds of Dichlor in 10,000 gallons would be 60 ppm FC and 54 ppm CYA so I'm not sure how you calculated how much to add. Did you use The Pool Calculator? This much Dichlor after usage of the chlorine would result in a pH of 6.6. That's probably what happened.

High chlorine levels (> 10 ppm FC) will definitely interfere with the pH test, but usually it causes you to think the pH is higher than it is, not lower. Read the Taylor booklet as it talks about this effect. So yes, I think your pH did truly get pretty low, but 3 pounds of 20 Mule Team Borax would only raise it from 6.6 to 6.7 or so. It takes about twice as much Borax by weight as it does pH Up (sodium carbonate) for the same pH rise, but Borax won't increase your TA as much. If your pH still reads at the bottom of the pH scale, add some more Borax.

Just don't add any more Dichlor (or Trichlor) since your CYA level is fine. Use chlorinating liquid or unscented bleach or even Cal-Hypo as your source of chlorine. With Cal-Hypo, for every 10 ppm FC it will increase Calcium Hardness (CH) by 7 ppm, but since your CH is low that's fine. Since you have a vinyl pool you don't need to have a high (i.e. 300 ppm) CH so using Cal-Hypo as a source of chlorine, for a while, is an option for you -- a decent option for shocking. With any chemical addition, just make sure it's done slowly over a return flow and sweep the side and bottom with a brush to ensure mixing. For Cal-Hypo, you may need to pre-mix it in a bucket since it is a little slow to dissolve and you don't want any settling to the bottom of your vinyl pool.

Richard

[yitbos1]

Actually, I shocked to 30 ppm, waited until the FC went back to about zero and shocked to 30 ppm again. I waited until the FC went back to the 3 ppm range before I tested pH again. I can see how the pH ended up so low now, though. More Borax is in my future...

I do not plan on using any stabilized chlorine products now that my CYA level is where I want it. I have a Liquidator coming soon (hopefully), but until then I will merely add bleach daily.

Thanks for the quick response, Richard!