I plan on starting a grow out tank in the very near future, and I am wondering what type of filter I should use in it ? It will probably be a 15 or 20L size. I was curious as to what type of sponge filters (if it is sponge filters) you guys and girls use, and if it is a sponge, what do you use for an air pump ? I have never used anything but an HOB filter on any of my tanks, and I know nothing about sponge filters. Any info would be greatly appreciated. Thanx.