I haven't even set up my aquarium yet but the instructions for my Eheim ecco 2234 say the canister should sit under the aquarium, 40-150 cm below the water level in the aquarium. I can't wait to see how it works.
The Eheim 2231 model is for up to 35 gallons. It has a stated flow rate of 127 gallons per hour. The Fluval model 104 for tanks up to 25 gallons flows about the same rate, 125 gallons per hour. Go figure. The Fluval is $13 cheaper at $57 USD. I bought the Eheim based on it's lower gph needed for the same size tank, and opinions read online.
