I'm in the midst of a prolonged "shock" cycle. Don't want to go into details. But, trying to understand the source of algae that may be gobbling up my chlorine in a clear, non-slimy, non-eye-irritating pool. Does algae reside in the filter? We use a cartridge filter with relatively low flow using a VS pump. Last time we cleaned it, a month ago, there was a huge amount of whitish residue, which I thought was from using Ca-hypo. No green or yellow. So, can algae accumulate in the filter??