Off the Chart Cyanuric Acid

[Watermom]

Even though a FC reading of 7 sounds high, for a pool with extremely high CYA, it is not. In fact, it is too low. You need to be keeping it between 8-15 ALL the time. Dropping below that is an invitation to algae. In your pool, each gallon of 8.25% bleach will add about 2.8ppm of chlorine. I think if it were my pool, when I tested in the evening, I'd add enough bleach to take it back up to 15ppm. The next evening, if you have dipped below 8, I'd take it a little higher. You want to add enough bleach so that you can make it to the next evening without going below 8.

But, first we need to determine if you have an overnight chlorine demand. If you do, it means you need to be shocking the pool. So, go ahead and try the overnight chlorine loss test I described in my previous post. Report your results back tomorrow morning. If you felt slimy, your pool is probably on the verge of an algae bloom.

Also, bump your ph up with some Borax.

[BnaRealtor]

Great. Heading to the store to buy some Mule Team. How much do you think I should add?

[PoolDoc]

ASAP, purchase (20) jugs of bleach, and (6) boxes of 20 Mule Team borax (detergent section @ Walmart), (1) gallon of DISTILLED water (not spring, treated, crystal, etc => DISTILLED) and a cheap OTO / phenol red testkit. As WaterMom cautioned, you are on the edge of an algae bloom.

Besides the dosing WaterMom told you:
+ ALSO add (3) boxes of plain borax . Add them slowly to the skimmer, while the pump is running. Do NOT choke the skimmer -- if you do, you can form solid lumps of borax that are hard to dissolve.

+ Retest your CYA, using 1/4 cup pool water and 3/4 cup distilled. Multiple the result x3

+ Retest pH this PM. If chlorine is > 10 ppm, test using a 50:50 dilution of pool water with DISTILLED water. (This only works with DISTILLED water; use tap water or other water, and the result will be meaningless.)

[BnaRealtor]

I added chlorine and three boxes of Mule Team.
Results:
FC 15.2
CC. 0
PH. 7.4
Total Alk. 100
CH 250

I followed the instructions for the CYA. 1/4 c pool water and 3/4 distilled water. From that one cup I took a sample and my reading came in at 35(x3)= 105. That's dramatically lower than the "off the charts" I was getting. Did I do that correctly? Happy it's lower but puzzled.

If this is the correct CYA now, then how high should my FC be?

Thanks for all your help. Please test my high school chemistry teacher I may finally be getting it...lol

[Watermom]

With a CYA of 105, your FC needs to be 8-15 ALL the time.

[BnaRealtor]

Tested FC again this morning before the sun was up. 13.5 ppm. A 2.0 drop overnight.

[PoolDoc]

Not huge; depending on whether you've been using the pool, or had a bunch of rain, could be normal. Or, with the chlorine up, you could be cleaning up debris somewhere.

But, check corners and crannies for algae or slime. And, keep your chlorine up (15 ppm) up for several days, and see if the overnight loss drops.

[BigDave]

... 1/4 c pool water and 3/4 distilled water. From that one cup I took a sample and my reading came in at 35(x3)= 105. That's dramatically lower than the "off the charts" I was getting. Did I do that correctly? ...

Bringing bad news - Sorry!
Diluting 1/4C pool water with 3/4C distilled, we need to multiply by 4. The pool water is a quarter of the volume we're testing. The result is CYA = 35(x4) = 140. Sorry.

It's OK to run the pool with CYA that high, just need to keep FC high enough.

[BnaRealtor]

I though it should have been x4..... Oh well. Now I I have misread my ph and adjusted it too high. It's at least 8. Guess I need to add music acid to bring it down? A small amount is what I have read.