High CYA after draining twice!

[Becca1984]

We moved into a new house and are first time pool owners. We noticed right off the bat that chlorine levels were so low we couldn't get them to register on test strips. After the bitter winter, we took our water in to a pool store and got it tested. All the levels were a mess but the big concern was CYA (150s). We drained the pool 1/3 and had it retested. CYA went down slightly but was still over 100 (130s). We drained again and retested. CYA was even higher (back in the 150s). We used test strips to confirm high CYA. We are at a loss. Do we drain for a 3rd time?? All other levels are good except slightly high alkalinity (per test strips). Also should add we are on well water. 

 

[waterbear]

What is your chlorine source? My guess is that you have a feeder that uses trichlor tabs and I will also guess that might have a cartridge filter, which is not backwashed. I will also guess that you might be shocking with dichlor.

Trichlor adds 6 ppm CYA for every 10 ppm of chlorine added. Dichlor adds 9 ppm CYA for every 10 ppm of chlorine added, Backwashing a sand of DE filter and winterizing a pool does help lower CYA a bit but bottom line is that most pools running on trichlor and/or dichlor will become overstabilzed.

On 4/22/2022 at 9:31 PM, Becca1984 said:

We used test strips to confirm high CYA

Test strips are notorious for inaccurate although precise results. Accuracy is the degree of closeness to the correct value, Precision is the degree of repetition of the same value under similar conditions. IE: retesting the same sample will give the same results but there is no guarantee that the tested result is right.

My recommendation is to ditch the strips and get a Taylor K-2006 test kit (Not the K-2005). It's worth every penny!

https://www.taylortechnologies.com/en/page/231/k-2006-complete-kit-with-fas-dpd

 

As far as the "drain and refill dance to lower CYA" goes it can take multiple partial drain and refill cycles to get the CYA into a workable range. Once solution is to turn your feeder to only add about 2 ppm FC and then use liquid chlorine or plain, unscented chlorine laundry bleach (both are sodium hypoclorite) to maintain the FC at the proper level, which depends on the CYA level. The higher the CYA the higher you need to maintain the FC for the same sanitizing ability.