I think we have mustard algae. We are new pool owners. Bought a house in October with a salt water pool. Just over 16,000 gallons. We have been getting the water checked weekly at our local pool store and following what they say to do. The water is actually nice and clear, but I notice a lot of yellowish brown sediment on the bottom that brushes away easily-seems very powdery. There is some staining on the walls, but we have been brushing regularly and it comes off fairly easily, but then comes right back. According to our water testing, we have had to add shock and muriatic acid weekly. (a bag of shock and a 1/4 gal acid) How can I find out for sure that it is mustard algae and what's the remedy?