Pool Chemistry Graduate School

[mooney1ak]

Everyone,

First thanks for all the help. This site has been a huge help in getting my pool back under control. When I took over the pool from our maintenance guy, I couldn't understand why he kept the chlorine so high (it literally created a yellow precipitate in my 5 in 1 test kit). Once I got the chlorine down to what a normal person would consider high, I started to get algae. Then I came across this site and learned about the Cl / CYA relationship. I got the TF-100 test kit and have reduced my CYA from 120 down to 60. I live in ATL and water is expensive so I'll probably wait until the Fall to get the CYA down to 40 - 50. In the meantime, the pool looks great and my wife is in love with the feel and clarity.

So bringing the rest of the pool into balance, my typical test results are:

FC 7.5 ppm
pH 7.6 - 7.8
CH 200 ppm
TA 60-70
CYA 60 ppm

What I've noticed is that I have to typically add acid to bring the pH down, but I usually have to add much more than pool calc says I should. For instance, I'll add enough for a .4 pH drop and only get .2. With the low TA I would have thought it would be easier to lower pH. Also with the acid add, my TA will drop into the 60 range.

I just recently added enough acid and baking soda to bring the pH down to 7.5 and the TA up to 80. Is it typical for the TA to want to trend that low? I've got a small water feature so I don't know if that is contributing to the higher pH / lower TA. We've been contemplating adding borates because of the water feature and perhaps as a fix to the low TA.

Thoughts?

Thanks in advance!
Ruben

 

[Texas Splash]

It's natural for your TA to continue dropping as you add more acid to control the pH. But I wouldn't try to increase TA too much at this point as that will only cause pH to rise quicker. Yes, the constant aeration from the spillover will certainly cause pH to rise. If you have a valve to slow that water flow down you might try that. As for the disparity in chemical dosages and changes in levels, is there any chance your pool volume is larger than 7500? When you add a chemical and it doesn't reach its target that would be indicative of a larger pool volume. Just a thought.

 

[Schadenfreude]

Another possibility, after you double-check your pool volume, is that your water already has borates. I had to increase my MA dosage after I added them. Have you ever used borax to bring up your Ph?

 

[Isaac-1]

Also how many hours per day do you run the fountain with the spill over water fall, aeration of water effects TA and pH

 

[mooney1ak]

Thanks, everyone. I'll order some borate test strips to see if borates are a possibility. I may be wrong on the pool volume. I'll double check with my next chlorine add.

The fountain runs with the pump so about 10 hrs a day. The way it is plumbed, I can only turn it on or off. I'll look into adding a valve to adjust the flow.

So it sounds like the suggestion is to let TA settle where it wants to even if it settles at 60. That sounds good. I just thought 60 might be too low.

Thanks everyone!