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

[HofstraJet]

aylad - I am in SE Florida and also have a pool in the sun all day. I plan on using your method of high CYA. What do you keep your chlorine level at and is there a downside to keeping it lower with a high CYA? Do swimmers find it uncomfortable?

Thanks!

[Watermom]

I'm not sure what chlorine level aylad runs but as far as your question about any down side to lower chlorine with high cya --- yes, ALGAE! Higher chlorine with higher cya is no more uncomfortable for swimmers than lower cya and lower chlorine. Take a look at the 'Best Guess' table in the link in my signature. It shows you the correlation between chlorine and cya levels.

[PBLsQuad450]

I was in exactly the same position when I found this forum. I found the partial drains to be a real pain. My chlorinator is just hanging out in case I decide to add CYA with Trichlor. You will jump right back up faster than you think, especially if you have a heat wave and those pucks turn chalky and vanish. You will have an algae bloom as well. And no decent way to deal with it because the high CYA and high enough Cl to shock will take forever to come down. Who wants the work of taking care of a pool you cant swim in? The pool just becomes unmanageable in my opinion. Sure, I have control issues. BBB satisfies them completely!

[chem geek]

There are other ways to deal with high CYA pools, but they involve extra expense using algaecides and other products. If one absolutely cannot (or is unwilling to) dilute the water or maintain a higher FC relative to the CYA level, then one can use PolyQuat 60 weekly both to control algae and as a mild clarifier (which you need because the lower active chlorine level breaks down organics more slowly). It still won't prevent algae if the chlorine gets to zero, but the FC level doesn't have to be as high as it otherwise would. Of course, this is extra cost -- usually around $2-4 weekly (after a larger initial dose) depending on the size of the pool.

I know that in my own pool years ago (before visiting this forum) when I was initially using Trichlor pucks/tabs I was also using algaecide, but every other week. My pool "turned" somewhere around 3 ppm FC with 150 ppm CYA. If I had been using the algaecide weekly then perhaps I could have gone to around 200-250 ppm CYA again with 3 ppm FC. So very roughly speaking, the algaecide may lower the minimum FC level from the 5-7.5% of CYA range to the 1-2% range, but that's really pushing it. You still have the problem that IF your pool gets behind the algae curve, then it still takes a very high level of chlorine to get rid of the algae since shocking the pool will tend to get rid of the algaecide more quickly so you're relying on the chlorine to get rid of the algae.

Yet another option is the use of 50 ppm Borates, but we don't have enough data to know how much it prevents algae growth. We know that it does as we've had multiple reports about that and I have it in my own pool now and have done some experiments, but my hunch is that it's not better than PolyQuat, but not that much worse either -- so a total guess on my part is that it would allow for something in the 3-4% FC as a proportion of CYA range, but I don't know exactly where in that range.

There are other options, but they have side effects or are not always effective. Copper-based algaecides kill algae, but can stain pool surfaces. Phosphate removers take the edge off of algae growth, but don't help if there are organic phosphates in the water, especially if the chlorine gets to zero at which point bacteria can quickly convert organic phosphates into orthophosphate.