CYA from 40 to 0????

[pzloo]

Hi All,

I tested my CYA about 11 days ago and got a reading of 40ppm. My pool was using more chlorine than normal (usually required 1/2 gallon a day, but was putting in a full gallon per day) so i decided to slam. Took my reading last night before bed and checked again this morning and loss of less than 1 ppm. Water is crystal clear. Tested again tonight and received a reading of 0 FC and 0 CC. Pool was uncovered all day. Checked CYA (in my kitchen since it's dark out) and received a reading of 0. I threw some more chlorine into the pool and will test FC & CYA in the morning before work.

Any idea what could be causing this?

 

[kellyfair]

You should check your CYA outdoors on a sunny day. You are going to get different results at different light levels. Stand with sun behind you and glance into tube after filling to each line. When dot disappears (at a glance, not staring into tube) that is your CYA level.

I’m going to guess that it was always zero or close to, and that’s why you can’t hold chlorine. But don’t add a lot until you are comfortable that you have an accurate reading. I always add in increments so I don’t add too much at once.

 

[IceShadow]

Before you add CYA, add enough liquid chlorine to get to 10ppm and test after mixing for 15 minutes. Let us know the FC and CC reading after that please.

 

[pzloo]

tested chlorine last night before bed. FC - 8 CC - 0. Tested again this morning and FC-8 CC-0. Water still looks as clear as a pane of glass.

Will test CYA tonight after work when the sun is out. My initial test where i received the reading of 40 was when the sun was out, back to sun with tube at waist high level.

i've had ammonia eat my CYA and chlorine before, but with no loss in FC overnight, my guess is that there is no algae/contaminants in the water. when i was testing before yesterday, i was losing about 4ppm of FC a day. i lost about 20ppm yesterday (solar cover off and sunny).

 

[IceShadow]

Very strange. Not sure what happened but adding more CYA after verifying there's none in the pool is probably a good idea. Maybe only 20ppm to start to ensure that there's not a smaller amount than the test will register to start?