I'm using Pentair Aquatics modules. One module for mechanical, one for biological and one for a heater. I built a double-decker stand for the tanks (to save floor space) and beneath that is the filter. On the way down to the pump I have a series of tees with ball valves. More tees and valves after the filter modules. Each tank has its own set of tees. When I add a new tank I just plumb it to an unused set of tees. My manifold is designed for a max of 12 tanks so I calculated a 4x per hour turnover rate for 12 tanks. I ended up getting a pump rated for 1200 gph (a liitle high) but since I'm only running 6 tanks right now, I didn't want to run 1200 gph until I'm up to 12 tanks. At first I was cutting back on the flow to each tank with the ball valves until an electrician friend of mine suggested wiring a rheostat to the pump which is basically a speed control for the pump motor. I got the pump at about half speed right now and when I add another tank all I have to do is turn the dial up a notch or 2 to continue to get my 4x turnover rate in each tank. That little dude is my favorite part of the system.