Adjust TA when chlorine very, very high?

[dawndenise]

I'm in the midst of a battle with what appears to be that hard-to-kill algae. I've been running my FC in the mid-20's, gone to 30 and just now added enough bleach to go to 35 . This is kinda scary.

My TA had been solid at 80 all summer until a test on 9/13 when it dropped to 60 for unknown reasons. Added 4# baking soda, tested out at 80.

Then the what-I'm-assuming-is-algae happened. In the midst of battle, my weekly test for TA was 60 again. Added just 1# of baking soda on Monday and Tuesday's tests showed no change in TA. Added 2 more pounds of baking soda yesterday and today there's still no change, still reads 60, maybe even 50 because the color changes are different at high chlorine levels.

Could my high chlorine levels be influencing my recent TA levels? Should I continue to add baking soda? Don't want to eventually have normal CL and find out I have too high TA.

TIA for any advice and input.

[chem geek]

Sandy,

Your TA will yo-yo along with pH, but even going from a pH of 8.0 to 7.0 by adding acid (or using Tri-Chlor) would only cause the TA to go from 80 to 67 if your CYA were 30. If your CYA were 100, then that TA would go from 80 to 61. So we can probably eliminate that TA/pH relationship as the main source of your drop in TA, especially if you measured the TA of 80 and 60 at the same pH level (did you?).

So that leaves carbon dioxide outgassing, but if that were occurring then you should be seeing a significant rise in pH that you have to counteract by adding lots of acid. Is this what you are seeing?

As for the TA test and interference from chlorine, you do add Sodium Thiosulfate drops as part of the TA test and this is intended to breakdown the chlorine because a high chlorine level will make the test go from blue to yellow (which is much harder to see) instead of green to red. To avoid this (if you see blue/yellow instead of green/red), just add more drops (say 4, instead of 2) of thiosulfate to your sample before titrating.

Last, but not least, what is your CYA level? The shock level you will need to kill the hard-to-kill algae (if that's what you have) is dependent on your CYA level.

P.S. When you add lots of chlorine, the pH will increase a lot as will your TA. As the chlorine gets used up (or if you add acid), then the pH and TA will get lowered pretty much back to where they were.

P.P.S. If you really do have this hard-to-kill presumed yellow/mustard algae, then it may take a chlorine level of at least what is found in the column "1.00" in this chart. If you have high CYA, this could mean exceptionally high levels of chlorine to kill this stuff.

Richard

[dawndenise]

Richard...thank you for your reply. Your chart, in another thread, is what's prepared me for the chlorine levels I'm now using - but I'll get to that.

My drop in TA on 9/13 was measured at a ph of 7.8, my previous "normal" of 80 throughout the summer was at a pH of 7.5. Just prior to the 9/13 tests, actuallly on 9/7, I ran a pH test with the Wally World HTH kit and also with the Taylor reagent from Ben's kit. With the same water sample, the HTH measured 7.5, as it had been for nearly the entire summer but the Taylor measured 8.0, maybe higher. The HTH kit HAD measured higher pH values accurately (I'm assuming) in early summer when I first tested my new pool's water.

Since then (9/7), I've been adding small amounts of muriatic acid every few days, if not almost daily and have yet to see a nice solid 7.5, as this summer. I recorded today's test at 7.5 (almost) but with no MA additions today, I'll bet tomorrow it'll be at least 7.8.

Looking back, maybe all my TA drop is from the additions of muriatic acid. After running such a stable pH all summer, I haven't had to remember that concept because I added so little MA all summer and my TA stayed right at 80.

Outgassing...I do have a waterfall that, previous to this algae, had been on 12 hours a day. I had absolutely no problems with stable pH during the summer. The only change I made in early September was to run the pump (and waterfall) for the majority of time in the daylight, rather than overnight and drop the time to 10 hours. Right now the waterfall is off to make sure all water is running through the filter.

My CYA measured 50 or slightly higher on Monday's test. Like most new pool owners, I struggle with consistency - at times, I've measured it at 40. I did recheck and can say that I've added 10# of CYA since the pool was finished in June. With no draining or backwashing (cartridge filter) a CYA of 50-60 is probably correct.

Your chart, comments, and the experiences of other forum members have helped a great deal, as I would have never expected to have to go over 20 FC to clear up my pool. Not that it's clear....yet. Going to 35 or a little higher MAY have been just the ticket; I'll know more in the morning when the light is better. Having never had algae and having never had a pool before, I still can't say for sure that algae is what this is...but it's my working theory.

IF both pH and TA should return to lower levels when the chlorine returns to more normal levels, what do I do in the meantime? Do I just keep trying to keep pH and TA somewhat in balance while my FC is so high?

[chem geek]

IF both pH and TA should return to lower levels when the chlorine returns to more normal levels, what do I do in the meantime? Do I just keep trying to keep pH and TA somewhat in balance while my FC is so high?

A higher pH is actually beneficial to killing the algae (there is less disinfecting chlorine, but the algae cells take it in more at the higher pH), though it shouldn't go above 8.0 or your pH test kit limit. So yes, you may need to add some acid during this high chlorine period and you'll have to keep the chlorine high so will have to continue to add chlorine (let us know the chlorine usage, especially overnight, as this will be an indicator of how much is getting used to kill the algae). You shouldn't need to keep adding acid once you've got the pH where you want it.

After the algae is killed and the chlorine maintains its level overnight, then you will let the chlorine level drop (get broken down from sunlight during the day) and you'll need to add base (Borax) during this process, especially if your pH gets down to 7.0 or your pH test kit limit.

It is not terrible if you just ignore the above advice and just keep the chlorine high with whatever its high pH is, but it might take even more chlorine to kill this algae under such conditions.

I'm a bit disturbed by your inconsistent pH readings. It's difficult to accurately measure the pH when there is a lot of chlorine (> 10 ppm) since the indicator will turn dark purple above a pH of 6.6 and this can be misinterpreted as a dark red so that you think the pH is higher than it really is. You could add some drops (2-4 drops) of sodium thiosulfate (the same stuff you add at the start of the TA test) and then test the pH, but the thiosulfate breakdown of chlorine is an alkaline process so will generate a false high pH reading (but you can just subtract about 0.1 pH from your measured pH for every 2 drops of thiosulfate as an approximation). If you happen to have "acid demand" drops, then you can try adding these after you take a reading to see which direction the color goes. Try the "acid demand" drops and see if the colors change from the high pH red to the low pH yellow.

Richard

[dawndenise]

Hi Richard,

Unfortunately, no demand drops to try.

This situation is both aggravating and intriguing. Up until yesterday, my FC readings weren't dropping any more than one would expect from sunlight; no big, big "chlorine demand," yet my pool water was a mess. So I decided to keep upping the chlorine just based on the look of my pool.

That trend of really no chlorine demand and 0 CCs existed until yesterday afternoon. In the AM, my FC was 30.5 with no CCs. Per another post of mine, I also turned my SWCG back on - 30% level - pump on 24/7. Still, because my pool really hadn't changed in appearance from the day before, I added enough bleach (182 oz) to up my chlorine by 5. Expecting about 36 at 2PM, instead I got a mere 31.0 and minimal CCs.

I added another 182 oz of bleach. Expecting something in the neighborhood of 36 at 7:30PM, instead I had only 24.5 with CCs at less than .5. This was the very first time I had seen a big chlorine demand. Sure, there was sun on the pool, but that had been the case the last few days as well and no significant drop in chlorine like this. By 7:30, I had also been able to smell some chlorine in the air. I also thought I saw the beginnings of some blue and some clearing coming back to the pool, but it was getting dark.

I upped the SWCG to 50% and also added 237 oz of bleach to take my readings back up by 12.5, to the over-35 range for overnight (take THAT, you algae! ).

This AM, my FC is at 38.0 with 0 CCs, as if things stayed pretty stable overnight. Pool is definitely clearer , as I can just about see the Phillips head screws in the drain covers.

I'm going to keep the chlorine levels up until my pool looks crystal clear everywhere like it did 2 weeks ago. I'm thinking of staying in the 35-ish area, which also coincides with your chart!

pH was at least 8.2 this AM, TA 50. Had already put in MA before I came to read posts so may actually be lowering my pH too much. Will try the sodium thiosulfate and see how much I screwed up.

[dawndenise]

The saga continues.

Chlorine only dropped from 38 yesterday morning to 35 by 2PM. pH measured about 7.6-7.7 w/sodium thiosulfate drops first. Added 91 oz (1/2 jug) bleach to raise chlorine to about 37.5.

By 6:30 last night, pool continuing to look clearer in the shallow end, still hazy with greenish/yellowish tinge in the deep. Had high winds all day so a lot of debris came in - just what I needed . At 6:30, chlorine was 32 and CC less than .5. Added 2 jugs (364 oz) of bleach to raise CL level by 10 to about 42 for the overnight.

This AM, pool 99% clear in the shallowest sections and clear on edges of the deep. Sun came on the pool and the middle sections and deep end still a bit hazy with that light greenish/yellow cast. FC was 43.5, CC less than .5 and my pH w/4 drops sodium thiosulfate, was over 8. First time I was actually seeing a purplish color in the tube. TA fell and is now at 40.

Added about half gallon of muriatic acid. Will let circulate for awhile and then add 2# baking soda. Won't put me where I want to be, but I can't help but think that my pool can't take being out of balance with super high chlorine, extra low TA and high pH for that much longer. This is such a different situation that what I had all summer.

As long as I'm seeing that light greenish/yellowish cast, I still need to keep up my CL levels, right? It's just hard to believe that anything could be growing in there at those levels.

Does anyone know if an algaecide is of any use as a preventive measure against this stuff?