Make-up Water:
Fresh water used to fill or refill the pool.
Multiple Filter-Control Valve:
A multi-port valve having at least 4 control positions for various filter operations. This combines the function of two or more single direct flow valves into one unit.
Muriatic Acid:
The commercial name for hydrochloric acid. (See Hydrochloric Acid) For a safer alternative, try Blue Wave's pH reducer available in 6, 15 and 30 lb buckets.