I am going to build a Nilsen Reactor for Kalk and wondered what your recommendation for size would be. I have a 36 gallon Cube, 15 running gallon sump. The tank will be mainly sps and lps, acros, montis and other lps. Stocked fairly heavily. The reactor can be no taller than 18" including fittings. I was thinking of using either 3" or 4" pipe to build the reactor. The 3" Would hold about 1/2 gallon and the 4" about a gallon. My ato will hold 4 3/4 gallons with the 4" or 5 1/4 gallons with the 3" reactor. How much volume do I need? Any recommendations?