06-04-2020, 08:01 AM
Join Date: Mar 2020
| | Re: Ever heard of a plenum?
Originally Posted by mistergreen
I just recently heard of it. It's a gap of space under the substrate. It's basically an under gravel filter but no uplift from an airline or pump.
The idea is to provide low O2. No O2 is when anoxic condition occurs. It would work for dirt substrate too if you layer a garden fabric so the dirt doesn't fall through.
I have two tanks, a 65 and a 6 (Fluval Edge) with plenums under a deep substrate of a mix of Oil-Dri (baked clay absorbent) and Eco Complete (about 3:1). The 65 gallon has a 3" bed with a 1" plenum and the Edge has a 1.5" with a .75" plenum. These tanks are 2 years old, moderately stocked with fish, snails, shrimp and plants. Both have HOBs.
My thoughts on the process came from reading up on Jaubert, Novak and the video series from Jay's Aquarium which I highly recommend for a plain explanation of the anoxic denitrification process, which is the whole point. From a reef perspective (which I'm not), I also drew on the GARF group who advocated a more open plenum system meaning more water circulating. The freshwater systems I'm experimenting with only have access via migration through the substrate and separating mesh.
In retrospect I'm not sure a plenum is needed, maybe only the deep substrate but I'm a believer in anoxic conditions for denitrification. My nitrate levels run around 20-30 ppm which I find very acceptable. I don't do a lot of water changes, maybe 40% once a month or so, and I don't do a lot of gravel vacuuming as a lot of waste breaks down naturally and is absorbed into the substrate. I'm on a well and use that water from the faucet. It's by then passed through a Whirlpool household water softener and a GE whole house filter.
My plants and animals are thriving and healthy.