Don, what type of cover do you have?
If you have a solid cover (held down by watertubes, usually), there shouldn't be a need for any bleach nor poly60 - the cl isn't being burned off by the sun and nothing's entering the pool water. Of course this assumes a clean, ballanced and shocked pool proir to closing.
If you have a mesh safety cover, you'll probably want to check the water every couple of weeks until it starts to freeze (and do the same in the spring when the water starts to thaw). It's not very hard to peel back a corner to test/ inspect the water. If you decide you want to add some bleach or algicide, I'd peel back one side of the cover and pour the chems at arms length into the pool, (a gal jug should require walking from shallow end to deep and back while pouring it in)
If you do decide to add more chems, using a 'sump pump' or similar will help disperse the chems more quickly (put the pump in the pool and have the flow going into the pool and pour the chems into the flow), but if you don't have one you can trust basic physics to distribute the chems throghout the pool.
As for the safety of the liner, I wouldn't sweat it, while there may be a high concentration of cl temporarily, it shouldn't cause any discernable damage to the liner, if you add the way I've suggested.
If you have any ?s about what I've said, I'll be more than happy to answer them ( the forum's a little boring at this time of year but I've finally got lots of time to devote to it)
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