As some of you may know I recently experimented with growing HC emersed, but as it was not working I added some NH3 to the water I was spraying the plants with to see if that helped (it didn't BTW). I did a NH3 test on the water that was in the tank 24hr after it got a spray and the test showed no NH3. I can only assume this was either used by the plants or got converted to NO2 or NO3 by bacteria in the gravel (I didn't think to test for NO2, idiot). Anyway, now that I've flooded the tank, it got me to thinking, in a fully planted tank with a moderate fish load, is there any need to have a filter other than for mechanical filtration? I.e. the plants do all the NH3 and NO2 filtering for you? Similar to live rock in marine tanks? At the moment I just have a small power head pushing the water around the tank with no form of biological filter at all. Granted I have no fish but when I add them would there be a need to add a form of biological filter or would the plants take up the slack happily without it? I would still need to maintain the water movement around the tank. Just some Sam ramblings, if anyone has any views/thoughts? Sam PS - I've got a great CO2 set up. The diffuser is fixed below the powerhead (I say powerhead its just a standard internal head just with the sponge chamber removed) so the tiny bubbles get sucked into it and chopped up into even small bubbles (almost too small to see), these then get pushed around the tank. Diffusion has to be near 100% and the bubble rate is far lower than I've previously run on the tank. I'll get some pics up if people are interested.