Why add CYA at all?

Hi All,

Thank you for this forum. I've spent some time reading through and have a couple of questions. :p

We just moved into a house with a 15,000 in-ground concrete pool. Although I've never had a pool before, I keep a freshwater planted aquarium, so the water chemistry stuff is very familiar. We're just outside of San Antonio so lots of alkalinity and a relatively high pH, both easily (EDIT: Well, maybe not the alkalinity) controlled with muratic acid.

The pool had -never- been drained before, so to get back to a known starting point it is now a few inches from being refilled. It has an auto-chlorinator and I have a little more of the Bioguard 3" trichloro-s-triazinetrione tablets. I'd rather stick with tablets (I'll probably go generic) since adding bleach every day is a non-starter for a variety of reasons.

My question: Since a pool consumes 1-2ppm chlorine each day anyway, and I can run the filter on a timer to add that during the sunny part of the day, and 1-2ppm works best at near-zero CYA, why do I need to add CYA to get it up to 30-40ppm? Why not just let it build slowly using the tablets, and then do water changes to keep it low?

Thanks,

Tom

You can do it that way, but it will take a while for the tablets to raise the cya to where it will maintain chlorine in the sun - but it will work if you can maintain the 1 - 2ppms of chlorine. You will have to keep tabs on the cya, because as it raises with the tabs, you will have to keep a higher chlorine reading. If it isn't a problem to change your water, then it should work for you - that is what is best - the routine that works best for you. You will have to watch your ph, as the tablets are very acidic.

Some people are successful with that method, although the water changes do get expensive after a while, particularly if you don't get much rain as makeup water. Also, once you do a partial drain/refil, you have to re-balance the water again, which takes more chemicals (more $$) and is a pain to do. Not to mention, near zero cya will offer very little protection from the sun, so you'll be using considerably more Cl to keep your pool in the 1-2 ppm range.

Michael

Hi, Tom,

Good question.

Because the CYA from the pucks is added VERY slowly to your pool, the Cl will have little protection from the sun.

Just guessing, but I'd think you'll have test results of 0 FC every afternoon for a period of weeks. The FC that builds in your pool overnight may be enough protection (I don't think so) and/or the CYA may build faster than I think.

So, by adding the CYA up front, you allow the Cl to keep your pool sanitized.

The constant addition of CYA thru pucks ('til the pool is overdosed) is one of the most common issues posted on this forum but that's for another thread.

If you have a cartridge filter or a non backwashing DE filter the CYA levels will build very quickly and you will have to drain and refill more often then with a sand filter or a backwashing DE filter. Just a thought to keep in mind.

Thanks All,

It's finally filled and I'll give it a while to stabilize. It has a sand filter with backwash.

Looks like the alkalinity is going to stay high at around 230ppm at 7.4 pH. What's the downside to the alkalinity being that high? I'm not going to change it, just want to know what to look for.

Thanks,

Tom

Hey,
If you add water weekly either by hose or rain i dont think you will have any problems as long as you watch the numbers. that is the system i use and my cya is always under 30, some weeks i float 1 3" tablet some weeks i float 3 3" it depends on how often i am around to put bleach in but i have never had a problem with cya getting 2 high. hope that helps

If your Alk is that high and you have a lot of Calcium Hardness, you may have trouble with cloudy water. If you drop your PH a little and get some aeration going, you can drop the alkalinity, but you'll probably have to keep after it if your fill water is that high. It doesn't take a lot of CYA to reduce your chlorine demand substantially, you might want to run the feeder pretty strong and run the pump into the evening a bit so you have some chlorine in the pool overnight to keep things well sanitized. With very low CYA, I'd shoot for a reading of 2ppm over night (measured in the AM) with a residual of about 1 ppm remaining as the sun comes off the pool in the afternoon. I'd test 2 x per day (AM and PM) unitl the CYA starts to build and you are able to turn the feeder down some.

The good thing is your pucks will lower your ph and when it gets to 7.2 , you can aerate your water by aiming your return jets up, the alk will lower as it raises your ph. You can continue to do this till you get to the alkalinity of 80 - 120.

Thanks All, again,

I went ahead and bought some CYA and have a small quantity in a sock in the skimmer. Is there a downside to targeting about 15-20 ppm and then letting the pucks bring it up slowly from there? I did have low chlorine (0.5ppm) after this first day after the refill, but it will take a few days to set the chlorinator.

BTW, if I use a cost of $100 per 40 pounds of tablets, that's about 15 cents an ounce, and for a 15,000 gallon pool I've read I'll be using 3 ounces a day to keep 2ppm chlorine, so 45 cents a day. Bleach at Walmart was $2.30 for 1.5 gallons, and a half gallon makes 2ppm chlorine in the same pool, so 76 cents a day. I must be calculating something wrong? :confused:

TW

The problem is that as your stabilzier levels increase you need to increase your FC levels to keep enough 'active' chlorine in the pool. You then use more pucks which then increase your stabilzier levels even more.
Check out this thread for info on chlorine levels and stabilzier
http://www.poolforum.com/pf2/showthread.php?t=365