The background varies from 3-7 cm from the back of the tank..depends on how the rocks are shaped on the background..You put rists in one end, and a powerhead in the other, full it up with bio and blue filter foam, and you have a big filter. i just did some math, and 5x200x60 = 60l filter..
The risk is that you COULD get deadzones behind there, wich can couse spikes, but its not very likely to happen..