CYA in a sock

[chem geek]

Personally, I've used an old T-shirt put into the skimmer and then added CYA on top of that shirt in the skimmer. It is important to note that my skimmer has a pipe going into the pool (looks like a return below the skimmer inlet) so that any skimmer clog will pull in water from the pool (and not crack the skimmer). I also have two floor drains so even if the skimmer and it's separate pipe to the pool were clogged, the pump would still be able to pull water from the floor drains.

So for me this works best as it is easy to do. The CYA dissolves in a matter of hours, usually overnight and certainly less than 24 hours. As for CYA measurement thereafter, at least 2/3rds of it registers after it dissolves (tested 24 hours after my last addition to the skimmer) and it could be more, but I don't usually add more than 20-30 ppm and target a CYA of 30-50 ppm so errors in measurement play a significant role here.

When CYA is added to the skimmer without a T-shirt, panty-hose, skimmer sock, etc. then it gets caught in the filter. The water velocity in the filter media itself is MUCH slower since it is spread over a much larger area. This is why it takes longer for the CYA to dissolve using this method. For my oversized cartridge filter with four 85 square foot filter cartridges, even with the pump at 48 GPM for my solar (it's 26 GPM with no solar), over 340 total square feet of cartridge area the water velocity is around 0.2 inches per second. In my skimmer (with no CYA in it that obviously blocks the flow significantly), assuming 15 GPM and a 1 foot diameter skimmer area the flow rate is about 2" per second.

Those that use a sock over the return should probably periodically squeeze the sock to break-up and mix-up the material inside. I think that a sock over the return is far better than simply broadcasting the CYA around the pool, but I think that putting the CYA into the skimmer either with a T-shirt/panty-hose/skimmer sock filter or without (to get caught in the filter) are very reasonable alternatives. Just make sure the filter isn't backwashed too soon -- the recommendation to wait a week should be fine (or if a CYA test shows that it is all dissolved).

Richard