Efficiently adding CYA

i'm thinking this question is right in chemgeek's wheelhouse.

it's been unusually hot and steamy here in beautiful cincitucky this year, and based on comments from the louisiana contingent, i'm thinking it might be a good idea to bump my CYA up some, maybe to 40-50 or so. (i usually try to keep it at or below 30.)

obviously, i could just go buy some CYA and dump it in. but because i'm in no particular hurry, i'm wondering if it might not make more economic sense to accomplish this increase by using trichlor tabs. i figure i'm getting the chlorine i need and adding the CYA as a side effect. (24k gallons, by the way).

anyone know if this would work out to be cheaper? (in case you're wondering, i'm not in danger of not eating because of pool chemicals. i just find it a fun challenge to try to operate my pool as cheaply as possible!)

Certainly an option as long as your TA/PH is not too low. Given the pucks are acidic, the tend to draw PH/TA lower, but otherwise you have the right idea. Just keep an eye on your CYA levels weekly. Then switch back to liquid chlorine when you hit CYA 40 and assess your chlorine demand.

whether it is cheaper or not depends on several of factors. For every 10 ppm FC added by trichlor, 6 ppm CYA is also added. You will also lower he pH and TA somewhat so might need baking soda and/o borax. If you must add CYA it will have no noticeable impact on your current water balance. IF you already have the trichlor on hand go ahead and use it but if you need to buy it using CYA is cheaper in many cases.

that's what i was thinking. i keep some pucks on hand for when we're away for long weekends, so i figured if i already own the CYA, i might as well put it in that way.

I wrote a post on the Cost Comparison of Chlorine Sources that shows that chlorinating liquid and bleach are usually the least expensive sources of chlorine though Cal-Hypo can also be inexpensive in some areas. Trichlor is close behind but isn't as cheap as it first appears because of the chemicals needed for pH adjustment. Dichlor is more expensive and lithium hypochlorite is ridiculously expensive.

I also wrote a post on the Cost Comparison of Cyanuric Acid (CYA) Sources that shows that accounting for the chlorine that you also get with some of the sources, the least expensive way to go is to use pure CYA though using Dichlor is close to the same and Trichlor is a bit more expensive. However, these differences aren't huge. At least with Dichlor, it dissolves quickly in case you wanted the CYA to rise right away.