How much CYA in trichlor tablets?

[jqgreen]

Hi,

10 year old 25,000 gallon IG pool. Never change the water, always used 3" trichlor tabs. his spring the CYA was 300+ (beyond the range of the test kit. pH ~7.2, temp, 74F, TA 140 Cl ~1 - 1.5.

Clearly water exchange is required. I am doing about 5,000 gallons a night during the week (about 12" drop). I don't want to do too much more because we have a high water table (~5-6 feet, and it takes forever to fill back up).

So here's the question: how much CYA is in trichlor? I'm curious so I can adopt a management plan for ongoing water exchanges to keep CYA levels lower.

Thanks!

[Watermom]

Generally for every 10 ppm of FC added by trichlor you are also adding 6 ppm of CYA. Having said that, I think you better wait until you have finished doing your partial drains and refills before deciding to use trichlor tabs. Unless you get it really low, you're not going to want to use them. It's a long way from 300+ to low enough to use trichlor. My guess is that you'll do better using some form of unstabilized chlorine. Depending on what your calcium hardness reading is, cal-hypo could be an option for you as well as bleach or liquid chlorine of course. Hope this helps.

[madwil]

6 of your partial water changes (at 5k, approximately 20%) will drop your CYA to about 25%- so from 300 to 75! like Watermom said, you may want to reconsider using trichlor on a long term basis...

[CarlD]

Yes, with your CYA at 75, using bleach and keeping your FC between 5 and 10ppm, you should find that you don't need to add chlorine as often, as long as you keep it in that range.

Carl

[jqgreen]

Thanks for the quick replies!

It must have been a long while since I had CYA in an acceptable range. I have a "tube" type auto chlorinator that holds 3" tablets, so I would prefer to use that. I guess I just need to keep an eye on the CYA and see when I need to change out some water.

Also, once I get the CYA where it belongs, does the addition of bleach occur fairly infrequently (i.e. every few days) because the CYA stabilizes it?

As an aside, I work for a water district with a water treatment plant, so probably should bring in a sample for the guys in the lab to go over - once I get it to what I think is dialed in. I'd hate to hear them say "hey look at the boss' pool water!'

[aylad]

One of the upsides to high stabilizer is that you don't have to add bleach as frequently. The downside is that, if you let algae get a foothold, it takes a LOT of bleach to get it shocked. I tend to run my stabilizer in the 80-90 range, but I live in Louisiana and my pool is in full sun almost all day. I add bleach every 2-3 days, but I also tend to keep my chlorine on the high side of the recommended range.

Janet