Effects of PH

[chem geek]

EricH,

I don't understand how your CYA isn't going up when using Trichlor. What's the size of your pool and do you have a sand filter that you backwash and if so, how frequently? Do you have lots of rain that spill over the pool to dilute it?

Do you have your own Taylor K-2006 test kit to test for CYA or are you using a pool store for the measurements?

Richard

[EricH]

I'm with you Richard, from reading this forum I always thought it should. I use the Taylor kit, and bought new CYA Reagent just to be sure, but that little black dot never even comes close to disappearing. For the record, I diluted the pool about 25% early in the season - see later for the reason.

I have a cartridge filter (that I've washed 3 times this year) and little rain enters due to the solid cover on the pool.

To stay on topic though: is low pH OK for concrete? Or as you're possibly identifying, maybe I've got testing problems.

One other potential gotcha: early in the year, I lowered the TA to zero with a mess of muriatic acid in order to remove some tough stains with Jack's Magic. It actually worked to remove the stains (that two visiting pool companies had failed to identify or do anything about) but definitely pulled some calcium out of our walls (thus the need for dilution.) Maybe that is still affecting the balance?

[chem geek]

Does your CYA test get even a little cloudy even though it doesn't obscure the black dot when the tube is completely filled? Are you mixing half (7 ml) pool water with half (7 ml) CYA reagent (melamine, actually) for at least 30 seconds?

You probably have at least some CYA in the water or else your chlorine would get used up very, very quickly. I just don't understand why it's not getting measured.

A saturation index of -0.2 is no problem at all.

As for pH and concrete, low pH is actually used during some processes (acid wash and initial curing) of concrete but after concrete is cured and stable it should not be exposed to very acidic conditions though it really has more to do with not having calcium carbonate saturation. Essentially with corrosive conditions (low pH, low TA, low CH) you dissolve the plaster/gunite/grout into the water, albeit slowly.

Richard

[EricH]

I shake it like a polaroid picture while counting to 30, and it does get slightly cloudy, just not enough to obscure the dot.

So even with my low pH, I guess my high CH keeps me in balance, so I guess I'll just keep doing what I'm doing. Thanks!

E

[chem geek]

Just so you know, I calculate -0.3 for the saturation index when using a pH of 7.0, TA of 100, CH of 400 and Temp of 85F and that should be the same as your Taylor watergram if you use an "adjusted" TA of around 90 though that doesn't make a big difference. You might try target a somewhat higher pH, but don't need to go to 7.5 -- 7.2 is fine. A pH away from 7.5 is more of a concern for stinging of the eyes. Also, when you get close to 6.8 or 7.0, then depending on your pH test kit you might not be able to properly measure that low -- anything lower than the lowest on the test kit will look the same.

Richard