CYA Through the roof?

[swilson]

OK, drained about 2/3 of the pool and filled with city water. Here are the test results:

CYA = 80-90
TC = .5
pH = 7.5
TA = 110
TH = 320

So, based on the pool calculator, it looks like all I need to do at this point is add bleach to get the chlorine level up. Should I only get it to the recommended level of about 4 or should I shock initially. My bleach jugs are 182 oz and the calculator indicates I should add about 1 jug to get it to about 5.5 and 2 jugs to get it to 10.

[aylad]

Wow, if a 2/3 drain resulted in CYA of 80 or 90, then it really was through the roof--no wonder you're having trouble getting it clear!!!
Is your water still green? If it's at all green or cloudy, then you need to shock it by adding enough chlorine to get to 20 ppm. You need to maintain that 20 ppm until it clears, then when you allow it to drop back down, keep it between 5 and 10 ppm--if you go below 5 ppm, you're going to have a really hard time keeping it clear. I know this sounds like a whole lot of chlorine, but that's unfortunately what happens when you have an overstabilized pool, and that's why in MOST cases, CYA of 40 or so is recommended. The good news is that with the stabilizer that high, it will be a longer time in between chlorine additions since the chlorine level won't drop as fast.

Janet

[swilson]

Still working on it but it looks like some progress is being made. Quick question, since I need to keep the chlorine level around 20 till it clears, what it the best way to test that, my kits only go to 5?

[chem geek]

You can dilute your pool water sample with distilled water (tap water usually has chlorine or chloramine in it) and then multiply your result by your dilution amount. So if you dilute 1:1 with equal parts of each, then multiply your result by 2. If you dilute 1 part pool water with 2 parts tap water, multiply the result by 3.

You should definitely get a good test kit. You can get a Taylor K-2006 test kit at a good online price here (the "C" version you refer to is larger in size so is more expensive, but you can get that for a better price here) or the TF-100 you can get here with the latter kit having more volume of reagents so is more comparably priced per test. A comparison of these two kits is in this post. These test kits use a FAS-DPD chlorine test that can measure up to 50 ppm FC, can measure Free Chlorine (FC) and Combined Chlorine (CC) separately and accurately, and can be as accurate as 0.2 ppm when using a 25 ml sample (when shocking, you usually use a 10 ml sample for 0.5 ppm accuracy).

[swilson]

Will it be accurate if I just double the sample from the pool and multiply the reading by 2, or triple the sample and multiply by 3, etc?

[aylad]

No, if you double the sample from the pool, then you actually have to divide your result by 2 instead of multiplying.

The sample from the pool should be diluted 1:1 or 1:2 with water that doesn't contain chlorine for the test to work--and even then you're going to lose some accuracy with each dilution...

Janet