Is there an ideal cyanuric acid level?

[Watermom]

You are most welcome.

[bobcat]

So maybe 60-70 for Central Texas?

[aylad]

I would start at 50-ish, let it stay for a week or so, and see how much chlorine you lose in a given day. Then bump it up to 60-70, and see if your daily chlorine loss lowers. If so, then you can stay there or maybe bump it up just a little more. If not, then it's not hard to backwash out 10-20 ppm CYA to get it back down to the 50 range.

I'm close to Shreveport LA, and I keep mine in the 80-90 ppm range, but my pool is in full sun all day. I find that with a CYA of 40-50, I lose approx. 4-5 ppm chlorine in a day. At 80-90, that daily loss drops to around 2 ppm.

Just remember that as you raise your CYA, you must also raise your minimum chlorine levels (see the link to the best guess chlorine chart in my sig). I know it seems like you're still using more chlorine, but once you get to your required baseline, it still uses less to replace 2 ppm daily than it does to replace 4 ppm.

[peatree]

Thank you again for your bountiful information. After reading several times, I finally "get" the necessity of keeping the pH so finely tuned. Thanks to:

http://richardfalk.home.comcast.net/...ool/OBrien.pdf

This was found reading your site. (It would be so satisfying to have found this on my own!)

The key features are
p 21. HOCl is 80 times more bactericical than Ocl(-)
p 23. The dotted lines for HOCl and Ocl shift with very slight pH shift, due to y-axis being logarithmic.
p 25. HOCl is more stable than OCl in sunlight.

Right now CYA is ~50 ppm and we'll see how it works out. As your site illustrates, it is easy to raise, but lowering is more difficult.

THANKS!

[PoolDoc]

If you read O'Brien, you should look for Richard (Chem_Geek) Falk's threads here in the China Shop, and at TroubleFreePool.com in the Deep End section, and get a copy of his spreadsheet.

I don't have time to get into it now, but there is not an "ideal CYA level". There are necessary levels of HOCl for effective algae and bacterial control. But those vary with CYA level, more strongly than with pH.

OBrien lays the ground work for that, but as far as I know, Richard is the only one who has covered it in detail. My own "Best Guess" chart was, and still is, the *practical* applications of those ideas, which I picked up from OBrien via John A. Wojtowicz, and combined with my own field experience. Richard picked the practical application here, about 10 years ago, and took off from there. He found OBrien, got a copy, and was able to get republication permission for a paper long out of print . . . which is why you were able to find it on his machine.

But, at least compared to the conventional pool industry, the BBB method taught here, DE-EMPHASIZES

the necessity of keeping the pH so finely tuned.

because, as you can see in OBrien, the HOCl levels are not nearly so sensitive as they are in a stabilizer free pool.

[Airren]

I have a CYA at over 100 - yes I am in the deep south, but I think this is not really good. How can I lower it?

[PoolDoc]

The only practical way to lower it is to drain and replace water . . . which is pretty wasteful and expensive, and which can destroy vinyl pools if not done professionally.

There is a way to drain in place, using a tarp larger than your pool, if it comes to that.

BUT . . . there is another alternative:

1. Buy a K2006 and find out what your CYA level really is -- you'll have to do a 1:1 dilution with tap water, test, and then double the reading. (Test kit info page, here. You'll also need the K2006 and CYA test in order to know how much to drain.)
2. Adjust your 'ideal' chlorine level according to the "Best Guess Chart" in my signature.
3. Chlorinate just one time per week with bleach or cal hypo (or get an SWCG)

Doing so is a lot less expensive than draining and refilling, and won't waste water. Your CYA will gradually go down over time, especially if you are backwashing a sand filter.