Testing CYA

Hey y'all,

Thanks to your good advice things are going pretty well with my pool. My one continuing problem is that I'm having to add what I consider a lot of bleach every day to get to my target level of 4. This is usually 78, 93, or 109 oz as the FC is 0.5-1.5. I'm thinking I need to boost my CYA substantially rather than keep it around 30-40.

This is where it gets interesting. Whenever I test CYA, I can always fill the tube to the top and still faintly see the black dot. I therefore think my CYA is less than 30. I have now run out of the CYA reagent, so I took a sample to the pool store -- and they measured 71!

FWIW, I know exactly how much stabilizer I've added since refilling the pool. I've added 4 lbs of CYA and one 13.5 oz bag of trichlor shock (66% trichlor). The pool calculator says my CYA should have been raised by 34.5. (I'm assuming it's really 9 oz of trichlor). That still makes my < 30 reading fairly inaccurate.

So what do y'all think? Could I be testing wrong? And given all the bright sunny days we have here in Tucson (often no clouds whatsoever) should I bump up my CYA to, say, 60?

Thanks,
Mike

CYA testing is a very subjective process--that's why you have to be careful to test exactly the same way, in exactly the same light, every time. You're really only getting a ballpark at best, but at least if your testing methods are consistent, you can pick up on any changes that have happened in your pool.

Regarding bumping up your CYA, that's a double-edged sword. I keep mine higher than most folks (around 80 ppm), because my pool is in full sun all day in very hot, humid climate and that's the only way I can keep chlorine in my pool. Keeping it that high drastically slows my chlorine loss so that I only add chlorine every couple of days instead of every day or twice a day, like I have to do with lower CYA levels. However, I do have to maintain higher chlorine levels to compensate for the high CYA. It might work out okay for you, but that's a decision that you have to make--but understand that if it doesn't slow your chlorine loss, then the only way you're going to be able to lower the CYA again is to drain/refill water.

Janet

Yes, having to drain the pool because of high CYA (~150) is what brought me to this forum in the first place. :-)

Is there really a realistic chance of it not slowing my chlorine loss? Why would that happen?

Mike

BTW, I took a second sample to a different pool store and they measured the CYA at 40. That's seems like a much better ballpark number to me.

Interestingly, I've now discovered on another pool forum they have an intro to BBB that reads in part:

"If you have a SWG or get extreme amounts of direct sunlight on the pool, adjust CYA to between 60 and 80. Otherwise adjust CYA to between 30 and 50."

So they have no qualms about recommending 60-80 for extreme direct sunlight. Here in Tucson with 105+ degree temps and no clouds day after day would seem to qualify.

OTOH, I'm not in a big hurry either. I think for now I'll assume I have 40 CYA and target 50 with a 6 FC target.

Mike

By bumping the CYA up just 10 ppm or so, you should be able to get an idea of whether it affects your chlorine loss or not. I can't explain the chemistry behind why the higher levels protect the chlorine better, I can only give you real-world experience gained from 8 years (and I mean year-round) of experimenting with my own pool.

Janet

I higher CYA level should have your chlorine last longer, but you'll need to raise your target FC level according to Ben's Best Guess CYA chart. The only real problem with the higher CYA level is IF you let the chlorine get too low and algae starts to form, it takes a much higher chlorine level to get rid of the algae. So you really need to stay on top of your pool maintenance.