I have an electric cover which is thinner than a solar cover and more opaque. It reduces the overnight temperature drop in half -- from 6ºF to 3ºF (when nights are around 55ºF and the pool starts out at 88ºF). It also cuts down chlorine breakdown (loss) from sunlight significantly. It also keeps all the junk out of the pool -- I forgot to close the cover this morning and my wife complained this evening about all the stuff that blew into the pool. It also keeps me from having to clean the cartridge filter (water is very expensive and sometimes in short supply where we live) more than once per season.

It is true that solar covers only last a few years and even the electric cover we have is only warranteed fully for 3 years and then pro-rated after that for a total of 7 years (so you can expect a life of 5-7 years). For us, the cover is worth it, but I can understand the hassle for some of rolling up a solar cover and the expense of having to replace it.

As for your original question about a solar cover and algae, I don't really know the answer. Following this forum's BBB method and Ben's chlorine table should prevent algae. A solar cover will still let sunlight in which algae could potentially use (while hopefully keeping out UV rays that breakdown chlorine).

Richard