# [Wet Thumb Forum]-What Are Your Thoughts on Plenums in Planted Tanks?



## Tenor1 (Mar 3, 2003)

Bob Goemans was the guest speaker Friday night at our marine club and described the use of plenums. I asked if freshwater planted tanks would have the same benefits. He had no direct experience but heard of success stories with cichlid and planted discus tanks. What are your thoughts? I will explain the plenum concept for those unfamiliar with them.

A plenum is similar (IMO) to an undergravel filter without having circulation through the system. It can be made using plastic egg-crate covered with screening material preventing the substrate from reaching the glass bottom. This creates a water space below the substate. Without trying to describe all the technical stuff (which I'd state incorrectly) this enables different specific types of helpful bacteria to occur at different levels within the substrat. The results are increased health benefits to the aquarium. Bob felt this would benefit plants as well as the fish.

This is a new concept to me and I would appreciate your input.

Regards,
Carlos 

PS- I don't have a marine tank but attend MASLAC meetings regularly as there are no other clubs in Los Angeles.

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I try to keep the tank plain and simple but it never stays that way!


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## Tenor1 (Mar 3, 2003)

Bob Goemans was the guest speaker Friday night at our marine club and described the use of plenums. I asked if freshwater planted tanks would have the same benefits. He had no direct experience but heard of success stories with cichlid and planted discus tanks. What are your thoughts? I will explain the plenum concept for those unfamiliar with them.

A plenum is similar (IMO) to an undergravel filter without having circulation through the system. It can be made using plastic egg-crate covered with screening material preventing the substrate from reaching the glass bottom. This creates a water space below the substate. Without trying to describe all the technical stuff (which I'd state incorrectly) this enables different specific types of helpful bacteria to occur at different levels within the substrat. The results are increased health benefits to the aquarium. Bob felt this would benefit plants as well as the fish.

This is a new concept to me and I would appreciate your input.

Regards,
Carlos 

PS- I don't have a marine tank but attend MASLAC meetings regularly as there are no other clubs in Los Angeles.

==============================
I try to keep the tank plain and simple but it never stays that way!


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## Wally (Aug 31, 2003)

IMHO and experience deep sand beds work much better than plenums in both Saltwater and Freshwater setups as they mimic nature as close as you can get in an aquarium.

The idea behind both ideas is to create a level in the substrate with very low to no oxygen. In this layer bacteria can grow that convert nitrate into nitrogen gas thus completing the nitrogen cycle. In planted tanks this fixes the nitrogen to the plant roots which acts like a fertilizer.

Problems arise however when high protein waste like fish poop and flake food rots in these low oxygen areas, this is what causes the black stinky anerobic areas that critics of the system complain about. These problems can be avoided however if you start of with clean sand.

In my setups I start off with about a 1-2 inch layer of Wal-Mart Brand "Special Kitty" Kitty Litter. This brand has very high iron content in it. On top of that I put another 3-4 inch layer of Quickcrete playsand
or Quickcrete "All Purpose Sand" depending on the color I am going for.

Just like in Saltwater tanks with Deep Sand Beds the most important part of this system are critters that will keep the sand mixed and stirred up just like earthworms. The best critter for this is hands down the Malaysian Trumpet Snail. Plant roots will also help the sand to stay a little loose. They will also bring down oxygen into the DSB to create little pockets of oxygenated sand which helps the whole process out. You will be able to see this as the roots will draw out the iron in the kitty litter and create rust around the roots.

Hope this helps I probably wrote to much.

*Don't feel like Satan, but I am to them...*


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## imported_aquaverde (May 5, 2003)

I'm under the impression the anoxic conditions remove nitrates. Seems undesirable in a planted tank.

James


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## Roger Miller (Jun 19, 2004)

Plenums are an old and controversial idea. In fact, some of my oldest tanks have plenums in them. If you looked at the tanks you would probably think they just had old, capped-off undergravel filters. But no! The wonders of modern aquaristics have tranformed the under gravel plates into plenums!

The major gain that reef keepers supposedly get from plenums is removal of nitrate. I'll set aside any question of whether or not they actually work or how they might work because there is usually little need for nitrate removal in a healthy planted tank.

Roger Miller

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_"The indispensible first step to getting the things you want out of life is this: Decide what you want" -- Ben Stein_


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## Tenor1 (Mar 3, 2003)

Thanks for the replies and clarification. Walley thanks for the detailed explaination and it wasn't too wordy. Aquaverde, Bob did mention the removal of nitrate at the talk but I forgot that part, lol. Roger, I'm glad you mentioned the UGF, because that's what it sounded like to me!

I suppose if using plenums were more beneficial then their use would be mentioned here. 

Thanks for the input,
Carlos

==============================
I try to keep the tank plain and simple but it never stays that way!


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## imported_RTR (Sep 11, 2003)

I have multiple plenum FW planted tanks, and yes they do remove nitrates. I got started with these a number of years back as components of veggie filters for high waste load fish tanks (I am a puufer nut) and they did function and do help.

Specialized diggers in FW are not readily available. MTS are very shallow diggers (oxygen limitation) and do nothing for the deep portions of the bed. Nobody is going to put gross diggers in a planted tank, I hope. But FW plenums at least can be fully functional without diggers, planted or not.

The object of the plenum vs DSB is to avoid profound anoxia (which is required for H2S, methane, etc., production) by providing open diffusion space and in theory to limit to sufficiently anaerobic conditions to reduce nitrate without going to conditions which would promote production of the nasties. The nasties will not make it to the substrate/water column interface in undisturbed situations, but unless you are a Diana Waldstad purist, most of us do replant, divide, or just re-landscape periodically. IMHO, comparing to wild conditions for tanks just does not apply.

I'm not certain that I see any significant benefit to plenums in conventional planted tanks, even low tech to near-low tech ones such as mine are. In higher tech tanks I would see them as likely to be detrimental, as they do eat nitrate, and thus would require additional supplement for no compensating reason. As an aid or adjuct to veggie filters, they do help.

These devices are also IME slow to start - it is months before the oxygen gradients and their bacteria are stable. 

If you do include the intermediate screen so often used in SW (to block gross diggers), the root entanglement will make you deeply regret it. My first trials with screen were short-lived. Any strongly rooted plant is impossible in this situation. My units are all of eggcrate light diffuser/PVC/fiberglass screen DIY construction. The oldest report I found on such a FW planted setup did use a capped-off UG plate as Roger mentioned.

"Where's the fish?" - Neptune


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