Need for filtration in planted tanks

While reading Steve's instructions on growing Ellodea, I had a few 
thoughts about need for filtration in heavily planted tanks. In 
particular, it seems to me that filtration may not always be such a 
good  thing after all. According to my understanding of the N-cycle, 
fish produce predominantly ammonia --- which is also what the plants 
prefer. A biological filter then  forces the bacteria to compete for 
ammonia with the plants, which is not a good thing. So it seems to me 
that it is better to leave it up to the plants to remove the ammonia and 
only remove the nitrates with water changes. 

I have a tank which has been running in this way for abot half year 
now. The tank is about 40 l and started with a few fancy guppies 
and a few corscrew vals. There is no filtration, no areation and no 
CO2 and the tank is lit by a single 11W fluo light. Usually I do one 
large water change 20-30% and often one small change 10% each week. 
Currently, the tank has a heavy load of guppies and lots of plants - 
both seem to do well and multiply even further. 

Comments? Suggestions?


Jan Fidrmuc

CentER for Economic Research
Tilburg University
P.O.Box 90153
5000 LE Tilburg, 
The Netherlands

Phone: +31-13-466-2678, +31-13-466-8221
Fax: +31-13-466-3066
Email: J.Fidrmuc at KUB_NL