chlorine consumption rate

[rimshaker]

My CL consumption has now increased from less than 0.5ppm/day (winter) to around 2ppm/day thanks to the summer weather. Does the CL consumption rate behave in a linear fashion or does it drop faster starting from higher levels? Like would it drop faster from 20 to 10ppm than it would from 10 to 0ppm? Or would it take roughly the same # of days dropping the same 10ppm amount? Thought I read about this last year, but can't find the thread now.

This is all assuming I have no algae bloom or anything serious.. just basic weekly maintenance. Pool is always balanced and clear thanks to BBB. Also my CYA is about 70.

 

[JasonLion]

Sunlight losses are a percentage, so you lose more the higher the initial level. Disinfection loses are constant relative to the starting level, so it doesn't matter what you starting level is. For most pools sunlight loses predominate, but a heavy bather load could make the disinfection losses significant. There are some more complex effects if your level is low enough to allow algae to get started.

 

[mas985]

Chemgeek will probably correct me if I am wrong but first order extinction rates are based primarily upon the percentage of chlorine. So for example at a CYA of 30 ppm, I lose about 50% of the chlorine during the day. It doesn't seem to matter much what the level starts at but the extinction rate of 50% is pretty constant.

However, what I have found is that if you double the CYA, the extinction rate goes down by more than 50% so you come out ahead with higher CYA.

 

[rimshaker]

Oh yea... thanks now i remember the thread.. something about maintaining CYA levels in the upper ranges I think.

 

[Florida Penguin]

Along this same line....

What is the safety level for swimming in a pool recently shocked. I am guessing that FC of less than 20 is probably OK. Anyone know what a true safe level of FC in a pool would be?

 

[JasonLion]

It all depends on your CYA level. If you have CYA in the water you can't get the active chlorine level high enough to be actually dangerous but you can perhaps get it high enough to start causing some minor problems like bathing suits fading and hair getting brittle. People swim in pools with no CYA and FC around 5 and the active chlorine level there is off the scale compared to a pool with CYA. The standard shock level corresponds to about a FC level of 2 without CYA, so you have some margin even with FC at shock level.

 

[TizMe]

How often should you be checking CYA levels? Our CYA levels have been between 40-50 consistantly with our CL levels staying betwen 5-6 (adjusting as needed). We have been checking lvls every other day, so is it okay to go to once/week checking CYA levels so long as our CL level is kept between 5-6?

 

[JasonLion]

I only check the CYA level twice a season, once to get it set correctly in the spring and again in early August. Unless there is some reason I suspect major water replacement, like a leak or major rains flooding the pool, etc, then check the CYA level an extra time.