Low TA high ph while trying to complete swamp remediation

[mumstheword]

I have made some good progress toward rescuing my pool from 'green swamp' condition. The water is now clear but there is some discolored area on the bottom that looks like algae stains and a few spots that appear to be black algae. The steps I have taken are as follows:
1. Removed all possible organic material from the pool (leaves, sticks, bugs). I put an old pair of panty hose over my leaf net so that I could capture finer particles in the net.
2. Completely disassembled my DE filter and washed all parts, reassembled and recharged with new DE.
3. Added chlorine (liquid bleach and powder calcium chloride - after dark - 2 days in a row to target FC level of 15
4. brushed and vacuumed sides and walls
5. ran pool pump (filter DE) around the clock

As a bit of background, last summer after I had been away, some dark areas (stains) appeared on the plaster that had not been there before. (The plaster is old and we have never had this problem before.) I suspect that the chemicals bounced around quite a bit when a friend looked after the pool while we were away. When I returned the TA was extremely high as were the CYA and CH. I suspect that the stains are due to metals precipitating out or scaling or both. (There appears to be some staining near the light fixture (rust?)- maybe I need a new gasket there.) I plan to try to use a Jack's magic stain test kit to verify this but will need to have a low ph and FC level to do this. I need to fix the algae problem first.

Whatever I do now, I want to be sure I do not cause more staining (whether due to metals or scaling) while I am trying to remedy the algae problem.

I have been trying to keep the pH low before adding more chlorine as I read on this site that low pH (around 7.0) at high chlorine levels can prevent problems with stains. But the TA is so low right now (60) that I wonder if I need to bring it up? If I add baking soda, that will also raise the pH, right? Should I add baking soda first and then muriatic acid? And then chlorine? I have been adding the chlorine after dark so that UV rays won't be a problem given that my CYA is a bit on the low side. I added some liquid bleach and some calcium chloride since my CH is on the low side.

What is an ideal pH for my situation (if I try to raise the FC level to 15 -mustard algae shock level)? I didn't notice a suggested FC level for black algae. What would you recommend?

Is there anything I can do to eliminate the stains that appeared last summer? Is my low CH a problem?

The temp today was high 44 F with forecast overnight low 27 F. I guessed my pool water temp based on this. The levels below are based on results from water sample tested at Leslie's this evening.

Thank you! :-D

FC 5.0
TAC 5.0 ( I assume this means that CC ~ 0)
CH 175
CYA 20
TA 60
pH 7.8
temp (of sample at Leslies) 58 F
Temp of pool water about 40? (a guess based on outside air temp)
25,000 gallon gunite (plaster) pool
DE filter

 

[JasonLion]

Re: Low TA high ph while trying to complete swamp remediatio

Welcome to TFP!

What chlorine test did they use? I bet they used an FC test kit that only read up to 5, which could be creating confusion. High FC levels (above 10-15) can cause false high PH readings. And any FC level of 5 or higher invalidates the total chlorine test result, so there is no way of telling CC. Worse, significantly high FC levels (above 10 to 15) can cause the PH test to give invalid results.

Chances are that whatever stains are going to form have already formed. If you were confident in your test results, I'm certainly not, it would be fine to raise TA to about 80 with baking soda, then lower the PH to around 7.5 with muriatic acid. The baking soda won't raise the PH much at all, and the muriatic acid won't lower the TA all that much, so this should be easy to do. You don't want to lower the PH down below 7.5 while CH is low and the water is cold, both of which argue for higher PH levels. Due to the FC level confusion, it is probably best to wait on this as the PH might already be 7.5, or lower.

Yes, you want to keep adding CH, though perhaps it is best to wait until after the shocking process is over.

 

[mumstheword]

Re: Low TA high ph while trying to complete swamp remediatio

Thanks for the response.

I'm not sure what chlorine test they used. Is it OK for me to add more chlorine tonight without first adjusting the TA? I would like to add the chlorine after dark. I know that chlorine will eventually dissipate over time as it reacts with organic material. I am quite certain there is more organic material in the pool based on the fact that some areas of the pool surface appear to have black algae spots.

Also, can you further explain:
Why it is bad to lower the pH below 7.5 when the CH is low?
" " " " " " " when the temperature is low?

Do these conditions result in scaling? Or erosion of Calcium? Or precipitation of metals?

I am trying to better understand all this so I can figure out how to avoid future problems. And what caused those stains that appeared last summer (from scale or metals) in the first place. In a house we owned previously, we maintained the pool ourselves for over 15 years without ever having the stains like those. It is all a mystery to me - but I know there is a logical explanation based on chemistry.(chemystery!)

Thanks for helping to demystify this!

 

[Swampwoman]

Re: Low TA high ph while trying to complete swamp remediatio

This is not related to your immediate question, but from your posts, it sounds like you are dosing to shock level but not sustaining shock level. Algae is more forgiving in the cold, but normally the "shock" process involves sustaining the shock level until all three "clear" conditions are met.
So to truly shock and clear the pool, you don't want to be letting it drop back down to 5 ppm of FC, or you've essentially interrupted the shock process. Hope that helps!

 

[JasonLion]

Re: Low TA high ph while trying to complete swamp remediatio

Sure, adding some more chlorine is probably fine. It would be simpler if you get a good test kit, one with a FAS-DPD chlorine test that can reliably measure FC levels up to shock level. Without that there is a fair bit of guess work involved, since you can't know just how high FC currently is so you don't know how much more chlorine to add.

You need to keep the water in balance with the plaster. Several factors influence the water balance, PH, TA, CH, CYA, Salt, Borates, Temperature, etc. PH is the most important factor, but all of the others affect things also. Roughly speaking, too acidic and it will etch the plaster, too basic and calcium scale will form. There are various tradeoffs you can make, for example if CH is high you can lower PH, and if CH is low you can raise PH to maintain the balance. Temperature also affects things in that the colder the water is the higher you want the PH. If you follow our recommended ranges none of this needs to come up. And even if you can't, you still have a fair bit of range to work with before there are problems. However, you have mildly low TA, low CH, and low water temperature, so you don't want the PH going to low or you will start etching the plaster. Metals are more sensitive to the PH alone, without much affect from the other factors.

 

[mumstheword]

Re: Low TA high ph while trying to complete swamp remediatio

Thanks for that explanation! I am assuming that the pH relationship for metals is the same as it is for the plaster - ie. the more acidic - the more the metals will corrode and be in suspension in the water and the more basic, the more they will precipitate out causing stains. Last summer, after the pool had been in the care of a friend, the TA was higher than I had ever seen. I think other levels were strange too but I don't specifically remember them. I do remember the TA because no matter how many drops I added, I couldn't get the sample to change from red to green. I realize that when other levels are out of whack (eg. very high chlorine) the test results may become inaccurate. I'm not sure if an algaecide had been added at that time - possibly one containing copper.

After I get the organic materials fixed (the algae) I want to try to work on the stains that developed last summer. I spoke with someone regarding the Jack's Magic Stain Test Kit and they said that it is possible to have metal stains covered by scale - which makes the stains difficult to remove. At least it requires a 2 step process. Any thoughts on that?

Thanks!