My understanding is that BleachCalc always shows liquids by volume and solids by weight. My calculator shows solids by both weight and volume, but the weights will be more accurate. Powders can be fluffed up into larger volumes or packed down into smaller volumes and ground differently so that they pack differently.
Well I was thinking of adding borax to increase Borates to 50. But with a 25000 gal pool, that works out to 92lbs of Borax and 5 gallons of Acid. This pool is in the Midwest so spring cleanup is always an issue. Now I just dont know what to do. Hum. I assume the Borax will only need to be replentished due to backwash and splashout.