More Fine Tuning

[Jersey Devil]

Everything seems to be going well in my first BBB summer, but just wanted to get a little fine tuning advice (or at least explore differing opinions, as I know that after a while pool control becomes quite a personal process). Saturday am numbers are:

FC 4.5
CC 0
TC 4.5
pH 7.6
TA 100
CH 70
CYA 30 (I had this up to 50 but had to drain twice due to heavy rains).

My questions are as follows:

(1) TFP-100 instructions recommend TA 100-120. Jason's Pool Calculator recommends 70-90+. I assume I am OK as is and that for my pool an acceptable range would be 70 - 120. In any case, I am able to maintain pH at a steady 7.5 - 7.6. Any adjustments needed?

(2) My CYA is now at 30 and I have maintained a 30-50 ppm range all season. I adjust FC accordingly to Pool Calculator mid-range value. No algae, sparkling water, etc. A+ rating from my pool inspector (wife). I find that I have about a 3 ppm FC loss due to sun and use no matter where in the 30 - 50 CYA range I am. I have read that above 20 ppm CYA efficacy diminishes. So.....what are the experiences/recommendations of the forum (and I will likely do whatever I think is best anyway )?

 

[Bama Rambler]

If your pH is fairly stable then 100 TA is your magic number.

I ran 50ppm CYA all last year and lost about 2ppm per day but this year I'm losing about 3ppm. This years extremely hot weather is the reason. I'll just live with it and hope for better next year. It's basically what works for you.

 

[257WbyMag]

An outdoor pool without a SWCG needs 30-50 ppm of CYA to maintain a FC residual to keep water safe and sanitary. The only time that I would see using a CYA of less than that would be in an indoor pool.

As far as the efficacy of CYA diminishing at levels above 20 ppm, I'm not entirely certain what that means.

 

[JasonLion]

I have read that above 20 ppm CYA efficacy diminishes.

The article that is from is misleading at best. As the CYA level increases the amount of chlorine lost to sunlight goes down. This continues to be true as CYA goes up to very high levels. Yes, there is a large reduction in chlorine lost as CYA goes from 0 to 20, and a smaller reduction in chlorine lost as CYA goes from 20 to 50. But that "smaller reduction" is still very significant.

With CYA at 0 you lose all of your chlorine to sunlight each day, perhaps 20 ppm lost to maintain a reasonable level. With CYA at 20 you are still losing more than 3/4 of your chlorine to sunlight each day, perhaps 5 ppm lost each day. With CYA at 50 you are losing perhaps 1/2, or 2 ppm a day. With CYA at 80 you are losing less than 1/8th, or 1 ppm a day. The improvement from CYA of 0 to CYA of 20 is a savings of 15 ppm of chlorine, obviously dramatic. The improvement from CYA of 20 to CYA of 50 is a savings of 3 ppm, nowhere near as large in absolute numbers yet still an 80% savings, which is also dramatic just a different kind of dramatic. (All numbers are approximate and will vary significantly from pool to pool.)

 

[Jersey Devil]

Check :idea: I did not see the entire article, just a quote from a poster. The quote is correct, however, in that the affect of CYA does diminish rather significantly, although the relationship is more linear than exponential. Then it becomes a trade-off between FC loss (and bleach cost) v. shock level. So, what I am hearing is 30 - 50 ppm, my choice (By the way, I am a jug dumper, no SWG as yet and maybe never.). Since I have yet to shock since going on BBB this would seem to favor the higher end of the range from a bleach consumption point of view. Since the objective of TFP is learning about how to care for your pool, this discussion has been helpful. I would appreciate any further clarification, the more data the better (but maybe Chemistry 201 is the place to be )