Hello :) First of all this isnt an octo tank question, its for my main reef tank. I'm just trying to get a variety of answers and you guys are so helpful! :) I have a 150G. setup thats been running for quite some time now, its a very mature tank. Since day 1 I have been running a reverse flow undergravel filter, a canister filter, a skimmer and tons of live rock. So lots of filtration in the tank. I was wondering how it would effect the tank if I removed the undergravel filter tubes. Just like a plenum it would create a dead space under the substrate. The idea is that the dead space helps in the denitrifying process. Will this work in my setup? Does anyone have experience with Plenum systems ? :) Any responses very much appreciated! Thank you.