Drain & Fill Question

[CarlD]

Richard:
I'm aware that if you drain off 200 gallons, then refill, your concentration of CYA changes. The next 200 gallons you drain will have a lower concentration so the refill will give you less "bang for the buck".

I deliberately decided to ignore that problem as it soon becomes an exercise in differential calculus--which I never use for fun or hobbies! I deliberately kept it SIMPLE for clarity.

I wanted to get to the REAL point: with excessively high CYA you cannot try to drain a little, then add a little to be effective.

Sometimes, trying to be very, very accurate causes you to obscure the REAL message and the real answer, so you have to watch for a "forest and the trees" situation: With excessively high CYA, if you want to lower it you must do a large drain and refill. Period.

The object is to give NJPool an effective option.

[chem geek]

I wanted to get to the REAL point: with excessively high CYA you cannot try to drain a little, then add a little to be effective.

OK, I got it. The main takeaway point I wanted to make was that if you want to do significant dilution, especially more than 50% (if you have very high CYA over 100, for example), then using a sheet or silage tube uses much less water and is much more efficient (for water usage, though obviously takes more effort). I just thought the 100 gallons 100 times (to get 10,000 gallons) would be misleading and let people think they didn't need to use the sheet method to be efficient. However, for just a 50% dilution, doing it continuously is certainly a reasonable option and is "close enough" to help get the CYA lowered (going from 100 to 61 isn't that far off from the goal of 50). If the goal was to go from 100 ppm to 25 ppm, then a continuous drain and refill of 75% of the pool water only gets you to 47 ppm. I'm sorry I was so picky.

Personally in my own pool, I dilute it each winter with winter rains filling in and overflowing (to a sewer drain) and that's a continuous method, but since I'm not paying for the water I don't care that it's not efficient (our water is very expensive where I live and is sometimes under restriction). I do this to continually refresh the water each season. I do need to add some more calcium, bicarbonate, and CYA when I open up in the spring. Now that I'm not using extra chemicals (non-chlorine shock, clarifier, polyquat algicide, de-foamers, etc.), this refreshing of the water probably isn't necessary.

Richard