I just cleaned my above-ground pool cartridge filter. The pleats were covered with a powder blue residue that washed off with the hose, but pooled on the ground — the only blue things I’ve had in the pool are one blue noodle (new this season) and a solar cover that looks like blue bubble wrap, which I am using for the third season in San Antonio, with temps around 100 degrees the past few months. Could the solar blanket be deteriorating?
It could be but that is not likely to be the cause of the blue powder in the fliter. This can be a number of different things usually related to the chemistry of the water and salts or metal salts. For example, copper is typically a blue color and can be reacting to cause the powder you are seeing.