A friend of mine has not opened his in-ground vinyl pool in about five years, and has decided to get it cleaned out this year. I believe it has a Hayward sand filter if I recall correctly. Needless to say it is currently a swamp. Since he was running Baquacil I'm going to recommend it be converted to chlorine at least long enough to clean up the swamp. I should be able to help with that since I helped convert my parents' pool last year, and I'm hoping that the Baq conversion process plus removing as much solid matter as possible will get a really good start on cleaning up the water as well.
My question pertains to the filter. He's had the pump running in recirculate mode briefly and it seems like all that plumbing still works, but he hasn't tried or looked inside the filter AFAIK. Is it likely the filter sand has solidified into a useless mass or something after sitting for five years? Obviously we need to change the sand, but I'd prefer to wait until any remaining Baquacil is purged and the swamp is mostly cleared up.
Any other gotchas I should watch out for? Thanks.