Under gravel filters

[Tuna Howard]

What if I placed a power head with a Pre filter on the top of my gravel filter out flow and run water down pipe and through the gravel?

[HH Morant]

I think flowing the water in reverse works, but it is not as good at aerating the water. If you pump the water in the usual direction, you can angle the flow towards the surface to provide good aeration.

See aquariumscience.org article titled "Under-Gravels in Depth"

[Tuna Howard]

Thank you for your reply

[Beardedbillygoat1975]

There are several UGF threads on the forum. There’s a tremendous amount of debate in those posts.  Low flow seems to be better then fast. If you do it slow it gives the bacteria more time to digest the waste and depending on opinions may lead to more anoxic conditions to get full breakdown in the nitrogen cycle but this is controversial. What isn’t controversial is Powerhead’s cause more debris to collect faster and then you’ll have to break it down clean it up and reset it again. By the way it’s disgusting! However it’s tremendous fertilizer for terrestrial plants. With an airstone low flow usually every 2-3 years you’ll have to do some cleanup. With a power head depending on the bioload could be 6-18 months. I haven’t had an undergravel filter in 20 years but they do work great. They’re making a comeback and are starting to get hard to find. 

[Tanked]

I don't know if I will ever understand the concept of a reverse UGF.  My first thought is: What will you accomplish by filtering the water before you filter the water? Two of the benefits of the normal setup are almost zero maintenance and nothing else to buy.