I have both an canister for main filtration and an undergravel filter for the fertilizer and water polishing in my planted 45 gallon tank and love it. Aquarium Co-op has a video on the undergravel and that is what got me thinking of using one for my planted tank. IF you are going to gravel vacuum like you should regularly the main complaint about the waste going to the gravel becomes more good thing as to me it is easier and cleaner to gravel vac than to clean out the HOB or canister foam of the food and waste. I mentioned water polishing or making it crystal clear and the undergravel does a better job for me than filter floss. For testing I was just turning off the power heads that I use on the undergravel. When its on my plants grow way faster with just liquid fertilizer regardless of type. I am using CO2 for the plants and that is the reason I am not using airstones and an air pump to run the under gravel.
Looking at a new tank and wondering if anyone has thoughts on making one from scratch as I want to do a 48 by 24 tank and not seeing one made for that size.
