I have seen it done - guppies with a plant in a completely sealed ball tank. The guppies eat the plant which produces oxygen and removes nitrates and CO2
from the water. The guppies remove oxygen and create CO2
and ammonia. On the bacteria side ammonia is broken down to nitrite and then to nitrate, which is back to the beginning of the loop. This is the ultimate in low maintenance with a just add sun approach.
I with this balance in mind would like do design my tank. I of coarse will feed the fish regularly to get things going, and ill cheat by giving my plants more CO2
but only because i want more plants than the fish population can support. The bacteria is in as external canister filter and in an under-gravil filter covering much of the 4' tank.
My thought here is i will be able to achieve an unnaturally high fish population if i have a large bacteria population as well as a lot of plant life. There will be more than enough airation and circulation!
What is everyones thoughts?