Maybe more CYA?

[Eva]

In an earlier thread about my covered pool (roof + vinyl cover, with ozonator, 9800 gallons) I was advised to maintain 20 or 30 ppm CYA. I got the TF100 and my CYA is about 20 -- it takes the entire volume of the tube before the dot on the bottom disappears. I am adding 12% liquid chlorine everyday (see details below) and I'm itching to increase the CYA to 30 and see if I can add a little less chlorine daily. I'll have to take it slow trying to get from 20-30, since even the marvelous TF100 isn't very precise when it comes to CYA.

So -- should I go to 30? As I said my pool is under a roof and has a vinyl cover, so it only gets partial sun for maybe a couple hours a day during the week, more on the weekend. It just seems like I'm adding a lot of CL, but I have no experience to know if this is a lot. And I'm thinking of switching to SWG, but not for a year or so.

I'm trying to maintain 3 ppm FC, but I haven't really got the pattern yet. FC seems to drop pretty sharply in 24h when I don't add any CL.

Any suggestions?

date	FC	CC	pH	CYA	CH	TA	Added
7/18	1.0	0.5	>7.6	20	400	100	10 oz 12% CL
7/19	1.5						22 oz 12% CL
7/20	3.5	0.5					nada
7/21	2.5	<0.5	>7.6				12 oz 12% CL
7/22	3.0	0.5	>7.8				10 oz 12% CL, 24 oz 35% mur. acid
7/23	3.0	<<0.5	7.6				10 oz CL
7/24	3.5	0.5					10 oz CL
7/25	4.0	<0.5					10 oz CL
7/26	4.5	<<0.5					nada
7/27	3.0	<0.5	7.6				12 oz CL
7/28	4.0	<<0.5					8 oz CL
7/29	4.0	<<0.5					8 oz CL
7/30	3.0	ND					10 oz CL
7/31	3.0	<<0.5	>7.6				10 oz CL

 

[woodyp]

Going to 30 won't hurt a thing. Just about anything less than that is a lousy mess of accuracy.

 

[chem geek]

Don't forget that your ozonator is consuming chlorine. Ozone and chlorine react with each other to produce chlorate, chloride, and oxygen gas. So maybe you should turn off your ozonator (at least you can experiment with it off vs. on to see if you notice any difference).

By the way, 8 ounces of 12% chlorinating liquid in 9800 gallons is only 0.8 ppm FC per day which is low chlorine usage. With a pool cover and a warm pool that is about normal since chlorine slowly oxidizes the cover (varies, but about 0.5 ppm FC per day) and also slowly oxidizes CYA (about 0.2 ppm FC per day) though the amount varies by water temperature.

Nevertheless, 3 ppm FC with 20 ppm CYA is on the higher side so would have more loss. So yes you could raise the CYA to 30 ppm and keep your 3 ppm FC target and probably lose a little less chlorine because the active chlorine level will be lower and there will be more CYA shielding the chlorine from the small amount of sunlight your pool gets per day. Just realize that you aren't using very much chlorine -- less than half of what most pools following TFPC guidelines use (which is 2-3 ppm FC per day), mostly because your pool is not exposed to very much sunlight.