Necessarry to drain pool and refill

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Necessarry to drain pool and refill

Postby spitz456 » Sun 22 Feb, 2009 21:25

Our pool maintenance man tells us that we have to drain and refill our pool because the water quality is bad. He says the algae growing in the cooler weather in Florida means that the water needs replacement. We suspect that it is just to make extra work and charges. Does anyone have experience with this problem?

chem geek
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Necessarry to drain pool and refill

Postby chem geek » Mon 23 Feb, 2009 02:30

It's more likely that the water isn't just "old", but rather that you have continued to use stabilized chlorine, most likely Trichlor pucks/tabs, and that the Cyanuric Acid (CYA) level has built up. For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases CYA by 6 ppm. Even a low 1 ppm FC per day chlorine usage would build up over 100 ppm CYA in 6 months unless you diluted the water a lot (backwashing helps, but is usually not enough to keep the CYA from climbing).

So you should first get a good test kit and measure your CYA and other levels. I recommend either the Taylor K-2006 test kit you can get at a good online price here or the TF100 test kit from tftestkits(dot)com here with the latter kit having 36% more volume of reagents so slightly lower priced "per test".

If you are going to continue to use stabilized chlorine and the CYA keeps rising, then you need to either raise the FC level or need to use a weekly algaecide (PolyQuat 60) or a phosphate remover in order to control algae. However, the least expensive approach is to simply switch to using unstabilized chlorine (e.g. chlorinating liquid or unscented bleach) when the CYA level gets to your desired level. You can learn much more about how to maintain your pool at the Pool School. You can absolutely prevent algae growth with chlorine alone, but need to have a minimum FC that is at least 7.5% of the CYA level (for manually dosed pools). In my own pool, I do this to prevent algae even though my phosphate levels are 2000-3000 ppb. The relationship of chlorine and CYA has been known definitively since at least 1974 as described in the paper shown in this link.


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