Hello all. After a 18 year break. I have a small, 45 gal corner tank. Not doing a lot of new technology updating. I went with what I knew back then. Under-gravel filter, and pump, air pump and air stone, and a small fluval 205 canister. And, two light housings on top.

The air pump, and stone are on a timer. And only come on for about 6 hours at night.

In the 7-8 months I have added a ton of live rock to it. Maybe 40-50 lbs?!? And, have just added a small skimmer that hangs of the back.

I must say. I have had very good luck, and so far. The tank is good, clean, and healthy. I have had no sick fish, or tank problems. I have aprox 8 fish, clowns, angles, butterflies, damsels, wrasse, cleaner shrimp, and some snails.

So, now the questions, or idea. My son, who also has a large tank, and reads much more that I. We talking the other day. He suggested that with all that live rock, and skimmer now. I should pull, or stop the underground piece of the tank. Just pulling the tube, and leaving the pump for circulation.

And I playing with fire, or just stay with what's working?

UG filters are pretty old school, I used them when I kept FO back in the 80's. I have to say that with my DSB, LR and skimmer I spend less time on tank maintenance that I seem to recall I did before. I think that UGF are probably OK if you are just going to have fish as they do a good job of nitrification. However, they can not go the next step and convert the nitrate to nitrogen gas. I don't know the repercussion of capping off a UG. Maybe it would just work like a plenum? What are your tank parameters?

Maybe it would just work like a plenum?

That's what I was thinking. I'd make real sure you siphoned out all the detritus under the filter before you cap it though.

What substrate are you using?

What substrate are you using?

I have a good 1" to 1.5" of gravel, and some crushed shell mater. What is "plenum"?

I have never used a plenum but here is an article Plenum - Description and Instructions (http://www.pgjr.alpine.k12.ut.us/aqua/plenum.html) that explains it. And, here is a good article them Advanced Aquarist's Online Magazine - Feature Article: An Experimental Comparison of Sandbed and Plenum-Based Systems. Part 1: Controlled lab dosing experiments (http://www.advancedaquarist.com/2005/6/aafeature) that compares them.