Sump size is all dependant on what you want your sump to function as. If you want a larger total volume for temp, salinity, etc. stability, then the larger the better. If you want it to function as a holding area for extra equipment, like skimmers, heaters, carbon, water topoff/dosing devices, then it should be big enough to handle this equipment. If you want it to complement the main tank by having an additional sandbed, algae bed, coral farm, refugium, then as big as you can sucessfully manage.
I suffered the same plight you have. A 38 gal tank/stand can only house a 10 gal sump(tank). I wanted more freedom. I designed a 20 gal long sump that sits on it's own stand next to the tank. If I had know before initial tank setup, I probably would have situated the sump behind the display tank.
My sump has three compartments, the first holds the skimmer and some rock, the second has a DSB, coral frags and caulerpa(lit opposite the main tank), the last has the return pump, more rock, and the kalk doser.
The most important function of a sump is to HOLD some of the water from the main tank in case of a power outage where your overflow sucks X amount of water out of main tank BEFORE the overflow siphon breaks or it reaches the bottom of your drilled overflow whichever is applicable in your case.
[ October 03, 2001: Message edited by: fishfarmer ]
[ October 03, 2001: Message edited by: fishfarmer ]
