The chlorine was at 0 when I swam, but I must say I only jumped in to cool myself off - didn't do any real swimming. You can always put polyquat in the water if you are afraid of an algae bloom while doing a stain treatment. The only thing I can think of is to put more sequesterant in than the bottle says. Keep your ph at the low level - 7.2. The green tint to the water may be that the walls of the pool are stained slightly yellow, which yellow and blue can make the water appear green. The only way to get rid of the stain that doesn't come off with the sequeserant is to do a stain treatment with ascorbic acid or oxillac acid. With a cya of 135, you must keep your chlorine between 8ppms and 15ppms. Your shock level will be 25ppms. Don't shock your pool with high ph - high ph with high chlorine will precipitate the metals out of the water onto the surface of the pool, unless you have enough sequeserant to bind to all the metal that is in the water.