Thanks for replying all!
I would like to reply:
I perhaps should have made clear that I am talking about
a) small tanks (that's the nano part of this forum's name), in which I would not consider goldfish, plecs, or any cichlids larger than an apistogramma. (My rule of thumb for putting animals in aquaria is that I don't like to see any animal in a tank that's more than one tenth of the tank length - so in my 18" tank 1.5 inches is the upper limit. I don't think that it's impossible to keep larger animals than that, but it looks wrong to me. Similarly in my small tanks I don't use any plants with large leaves.)
b) tanks that are set up to encourage optimal plant growth (the planted part of this forum's name), which to me means an aquarium with a decent depth of a suitable substrate for plant growth, sufficient lighting for strong growth, and availability of all nutrients needed, eg CO2 Iron etc., (certainly no airstone!). The oxygen in my tanks is generated by photosynthesis. I didn't make any of that clear in my original post.
Lastly, in the tank I'm thinking of the addition of CO2 keeps the pH below 7, so ammonia does not occur.
So to be a bit more specific, has anyone tried removing the filter, or just the filter material, from a tank set up as described above? As I said before, I'm talking about lightly stocked tanks with a decent substrate, dense planting, CO2 and trace element additions, and a light stocking lever - eg in my 18"x12"x12" 40l (10 US Gal) tank I have 2 Ottos (1.5"), 12 Green tetras (1") two sparkling gouramis (1.2") and 5 shrimps (1"). Plant growth is excellent, and I remove a couple of cups of plant material each week.
Thanks again to everyone who's responded so far!
Originally Posted by crazie.eddie
I'm sure it can be done, but the tank should probably be lightly stocked with fish that are not messy (goldfish, cichlids, etc.) or those that produce lots of waste (plecos).
Otherwise, if you stock it more heavily, I would assume that you would have to perform more water changes. It's basically the same principle as using undergravel filter of letting the benificial bacteria on the substrate to take care of the fish waste and the powerhead to keep the water agitated to keep it oxygenated for the fish. Also like using a sponge filter for the biological filtration and an aeriator (sp?) to keep the water agitated, which I've seen alot of breeders use, especially with a bare bottom tank.
I would just monitor the water parameters more closely and frequently, especially the ammonia and nitrite levels.