No, the water is not running through the heater. I have an electric heater - and a Sta-rite system 3 modular media filter. I just did the ascorbic acid for the second time because the first (12 pounds - for my 38,000 gallon pool) did not take out all the stains. But the water is too cloudy to see whether the stains are now out (I did it about 15 minutes ago). The PH is at 7.2, FC and TC 0, Alkilinity high at 180 and Total Hardness high at 250.