Besides filtering some of the gunk out of the tank, what do filters do for a tank? According to Aquadvisor, I doesn’t change the stocking capacity at all. ( I put two 40g filters on my 30g tank and the stocking level stayed exactly the same according to Aquadvisor) And as far as aeration, they do very little of that if you have the water high enough so it is not falling or splashing. There was an article on this on an Aquabid forum by one of the sellers who uses no filtration and I started to wonder about this.