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There's Got To Be A Way To Better Battle Cya


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i haven't spent hours on this forum (which rocks!!!) yet to see what info is here, but i struggle with CYA at ALL of my public pools that run trichlor tabs. my options are let it get high and then drain it every year, or drain it little by little, or hand add calhypo or something else once it starts to creep up. is there a better way?

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i haven't spent hours on this forum (which rocks!!!) yet to see what info is here, but i struggle with CYA at ALL of my public pools that run trichlor tabs. my options are let it get high and then drain it every year, or drain it little by little, or hand add calhypo or something else once it starts to creep up. is there a better way?

In a word, no. Best way wold be to convince them to convert to sodium hypochlorite and persitantic pump feeders or go salt. For every 10 ppm FC added by trichlor you are also adding 6 ppm CYA. Dichlor is even worse, adding 9 ppm CYA for every 10 ppm FC added. IF not then hand dosing with sodium hypo or calcium hypo is the best option. Realize that cal hypo will add 7 ppm calcium hardness for ever 10 ppm FC added. This may or may not be an issue but high calcium levels are easier to deal with by lowering TA and keeping close tabs on pH so it does not spike above 7.8

If the pools are using non backwashing filters the problem is made worse since there is no dilution from backwashing (worst case scenerio. IMHO, trichlor should never be run in a pool that has non backwashing filter, be it cartridge or bump type DE).

If the pool is in a climate that does not winterize the problem is even worse since there is no partial drain on closing and refiill on opening.

If the pool is in a climate that has an extended swim season (more than 3 months) or is heated to extend the swim season then the pool will most certainly become overstabilized before the season is over.

Since these pool are public and on trichlor it's pretty safe to assume they are outdoors so lets look at some numbers. Let's assume a light bather load and a daily chlorine demand of 2 ppm. That means every 5 days you are adding 6 ppm CYA to the pool. Let's be generous and say that backwashing removed 1 ppm during this time for a net increase of 5 ppm per 5 days or 1 ppm per day. Lets assume you start at 30 ppm CYA (lowest recommended level for an outdoor pool). In just one month your CYA has gone up 30 ppm to 60 ppm. This is livable. However, in two months you are at 90 ppm and you are seeing algae growing in the pool so you have the added expense of polyquat 60 and more work to brush all the algae. Perhaps the pool even needs to be closed for shocking and closing a public pool is always a problem.

In 10 more days you have reached the maximum level permitted in most localities for CYA in a public pool and have to close the pool to drain and refill.

Your alternative is to do partial drain and refills on a regular basis.

The downside to this is the expense of the water that is wasted and if you are in an area that is on water restrictions (like much of Florida has been) this presents another problem.

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