CYA and Chlorine

[kmb997]

My pool water looks good, clear blue. 21' round, 10,400 gallons?, vinyl liner, and 300lb sand filter.
fc 3
cc 0
ph 7.6
ta 100
cya ? I added 3lbs, about 3 weeks ago, and haven't tested it, yet.

I have been adding 43oz of 6% bleach every evening to keep my chlorine in the 3-5 range. Does this seem like alot to be adding. No one has been in the pool and I use the pool rover once a week. It does get alot of sunlight throughout the day, though. I know everyone's pool is different, but just want to see what everyone thinks. Maybe I should add more cya?

Thanks

 

[JasonLion]

That sounds about right. With fairly low CYA you often need to add 50% of your FC level each day. You appear to be right around there or perhaps a little under.

 

[kmb997]

Do you think adding more CYA will reduce my chlorine uptake?

 

[duraleigh]

Do you think adding more CYA will reduce my chlorine uptake?

It may a little but probably not much. Most pools seem to use around 2ppm daily so for a pool your size that works out to around 39 oz daily......not far from where you are now. You may cut that back a little but I doubt you could cut your FC in half. I haven't done the math for the cost of CYA vs. FC savings but my bet is it would be a money loser to up your CYA just to save money on FC. Now for the convenience of adding every other day instead of every day that may make it worthwhile.

 

[mas985]

Do you think adding more CYA will reduce my chlorine uptake?

I think it will reduce your chlorine consumption. The more CYA that you have in a pool, the less chlorine that is lost to UV even when you maintain a higher FC residual.

Last year, I ran my pool at several different CYA levels and here are a few data points.

CYA, FC Residual, FC Daily Consumption
30 ppm, 2.5 ppm, 1.15 ppm
80 ppm, 5.0 ppm, 0.38 ppm

I have much more data but the bottom line is that with a higher CYA level and even with a higher FC residual, you will need to add less chlorine each day. It is a bit counter intuitive.

Also, you have to balance the CYA level with how hard it will be to kill algae if you get any. The higher the CYA, the more chlorine you will need to shock and kill the algae.

 

[kmb997]

My CYA should be at 35, according to the pool calc. I'm going to hook up my Liquidator and see how that works before I add another pound and raise to 50. There probably isn't much of a difference going from 35 to 50?

Thanks.

 

[chem geek]

It does seem that the benefit is non-linear, meaning that there is a bigger jump going from 50 to 70 than there is going from 30 to 42 (both are the same proportional jump), but we don't know the exact points at which this occurs. It may also be that the effect is stronger in deeper pools (and possibly in pools with less vigorous circulation, especially at the surface, but that's just based a hair-brained theory of mine that has yet to be proven).