How much room do you have to spare under the stand? get Just keep in mind that bigger isn't always better. If you are keeping a skimmer, heater, and return pump among other items, you want to make sure there is enough room to remove them as well. I went with a 55g DIY sump for a 180g tank and I barely have enough room on top to remove everything if necessary. In hindsight, 40g would have sufficed with a little more wiggle room.