CYA of 160


Well-known member
May 25, 2007
My dad and his wife left on a 10 day vactation. I inherited the pool care :)

Long story short, they've been bent over and pool stored. I won't get into all the particulars, but they fired them awhile ago and I've switched them to bleach, so far, so good. Water clear (after 1 day of bleach), but fas/DPD testing tonight revealed:

FC- 8.0 ppm
CC0 0.0 ppm
TC- 8.0 ppm
PH- 7.6
CYA- 160 ppm.

I got the CYA using the dillution method. Had enough test sample to do it twice, came to the same result both times. Based on the 11.5% of CYA FC target, pool should be running at 18 ppm, but it's at 8 ppm and water is clear, has been for 3 weeks or so.

Dad doesn't want to dillute, thinks this is the last year for this pool (pool store torched his 3 year old liner with very low PH last year, and he doesn't think the pool can take another reliner, very old pool he bought used and will probably get a new one).

Since the water is clear and the CC is 0, are we probably ok? Being so far below the target FC, I'm not so sure...

Since he has one return and I sampled the top 1' of water, the next time I'm out I plan to take a sample from the bottom center, where the least circulation would be (24' x 4' AG round) and see what it shows. He does have some stuff on the bottom, I took a sample tonight and plan to let it settle to see what it is, but at this point it doesn't look like algae, more like the pics of the stuff in that other thread. The pool is in the country in a similar setting, surrounded by big trees.


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
You can often run a pool with too little chlorine for some time before you have a problem, but eventually you will have a problem and then it will be a significant project to recover from it. This is the pool store approach. If dilution is out of the question you might want to go with some of the other aspects of the pool store approach, notably it might be good if you put in some polyquat. With some algecide and a little luck it might be quite a while before you have a problem.

Note that Ben's chart says min FC of 8 ppm for that CYA level. I tend to go with Ben's numbers at lower CYA levels and Richard's at higher CYA levels. But there hasn't been that much experience at high CYA levels, for good reasons, so it is difficult to know which approach is closer to reality.

High CYA levels make things difficult in numerous ways. Shocking takes vast amounts of chlorine. PH tests tend to be inaccurate at target FC levels and other tests sometimes don't work at all. Measuring FC requires the full FAS-DPD test every time and requires patience. Measuring CYA levels above 100 can be problematic. (Keep in mind that the CYA test is something like +-15, and when you dilute 1 to 1 that becomes +-30, even if the test is repeatable.) You need to remember to use the CYA correction for TA when calculating the saturation index. And on and on.


Well-known member
May 25, 2007
Thanks Jason.

I agree, overall, high CYA is a PITA. I did find two bottles of polyquat in their garage that I figured I'd use up, and have decided to bump the FC to 18 and see how it holds. I did buy them the FAS/DPD stuff from dave, got two bottles as they're gonna need it :(

Hopefully I can get them to a higher level and it will hold so they are only adding the same small amount each night (currently .375 gallons of 6%).

We'll see...