If you put the Cyanuric Acid (CYA) in pantyhose in the skimmer basket, be sure to keep the pump running 24/7 until it all dissolves (which will take a while). CYA is about as acidic as Trichlor (pound for pound -- CYA is slightly more acidic) so if the pump isn't running and the CYA dissolves during that time, then there will be a locally high concentration of acid that will flow through your system when the pump turns on. It will be brief, but generally it is safer to either keep the pump on the whole time or to put the pantyhose in front of a return jet in the pool. Perhaps this is overkill since CYA takes so long to dissolve, but Trichlor also takes days to dissolve and we know that damage has been caused by Trichlor in the skimmer basket unless the pump is always running.
Pat's option (the first link caustik put in above) of putting the pantyhose over a return jet makes the dissolving go faster (24 hours) and is safer with regards to the acidity.
There are other options for adding CYA to the pool. There is a quick-dissolving and fairly pH neutral formulation of a CYA salt called "Instant Pool Water Conditioner" made by "Natural Chemistry" and may be seen at this link. I've never used it, but I've been in communication with the chemist who developed it so it's certainly an alternative (it's a sodium salt of CYA in a slurry). Another alternative is to use Dichlor since that is also quick-dissolving. Of course, that also increases FC, but chlorine is something you need to add every day anyway so doing a "shock" with Dichlor is one way to add a lot of CYA relatively quickly. I haven't checked comparative prices for these options.
Richard
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