Jump to content

The Plenum


Recommended Posts

In a prior thread of mine, Dr Novak's name came up.   I only recently started watching his videos on the plenum and this got me thinking.

Now because "life happens", my desire for any additional tanks is on hold for the foreseeable future.  But I want to ask now, because when the time comes, who knows if I'll have access to great resources like y'all.

I've tabled my 55 gallon for even further down the line.  I'm just going to go with a 20 long for now.

I can't pretend to understand the science.  But the basic benefits of the plenum are fascinating to me - namely, no nitrates, no need for frequent water changes, without crazy plants.  In the earlier thread, I pretty much gave up on the idea of using an UGF because I wanted sand (BDBS more specifically), and I felt the weed fabric would clog up at some point.  But with a plenum, the water is moving so slow that debris will likely not be pushed downward to the fabric and clog things up.

The plan I'm thinking of would be starting with a UGF at the bottom.  On top of that, put the baked clay (kitty litter or oil dri), then some kind of iron source - I think I saw plektec mention some kind of red clay powder.  Then on top of that would be the fabric.   On top of that would be 2-3 inches of BDBS.

The uptake tube will be just a little bit higher than the sand.   I'll have an airstone powered by the aquarium co-op USB powered one.  I hate using airpumps (the noise of a HOB is more pleasant than an airpump for some reason).  But I've read that this particular pump, meant for nano tanks, is pretty quiet.   Since the demand is very little movement, it'll give just enough power for what I need.

As this is just a biological filtration, I will utilize a HOB - I was thinking of the Tidal, for mechanical and additional bio.

I hope to use minimal care plants (low tech), so I was thinking of moneywort in the back corners.  I still don't know about lights.  I may just use the cheapest LED and make it work like an aquarium light.   But when viewing a tank, I like the incandescent.  (my 10g is an old aqueon starter kit with incandescent lights - the tank looks much nicer with it on).  

My stock for now I'm considering rummy nose tetras, and a couple of dwarf gouramis (at least one honey).  If the tank is stable, and I have the room, I'd like to add otos or corys.  I prefer the former, but the latter may be easier to care for.   I haven't researched how these can coexist, or if they even can fit in a 20 gallon, so someone please squash my dreams now before it's too late 🙂

The plenum intrigues me because I'm all about low maintenance.  If it works as advertised, it'll reduce the need for frequent water changes.   While water changes do provide a bit of de-stressing for me, with three little ones in the house, weekly water changes aren't practical.  My current 10 gallon is just once a month and I like it that way (nitrates never go above 10ppm, but I just want to gravel vac which ends up being a 50% water change).

Has anyone had a successfully working plenum?  Anyone had one that never worked or worked but then stopped working?

My thinking is if this doesn't work, or at some point stops working, I dn't have to tear anything down.  I just turn off the airstone and take care of it like a tank without a plenum.  Maybe then consider rehoming some fish to lessen the bioload.

Link to comment
Share on other sites

Hi Gideyon,

I'm running a slow moving plenum on a 45 long, two 10 gallons, and a 15 gallon "pond."

After my 45 long crashed and our "show" 10g struggled to balance out with a chunk of driftwood in the tank, I decided to give the plenum a try. They've been running for a few months now and it's been pretty fantastic. great plant growth and top notch water quality.

I recommend the oil-dri or Safe-t-sorb over the kitty litter. the kitter litter has some raw bentonite mixed back in to assist in absorbtion of kitty refuse, but it ends up shedding a good amount of silicates in a fish tank. if your phoshates creep up (from driftwood or fish food) diatoms tend to go gangbusters until the silicates get used up.

In my 45 long, all of my hair algae died when i replanted after adding the plenum with oil-dri. I was pretty baffled at the time. I couldn't grow bolbitis or any java fern beforehand as algae would overtake them pretty instantaneously. So that was a nice plus when i set it up. hair algae is starting to creep back in, but i believe it is because the plenum has run out of iron to help "take out" phosphorus and the plants cannot keep up with my generous feeding schedule.

I haven't fertilized my tanks since they've been setup so I may give "leaf zone" a go as Novak recommends potassium and iron as the main fertilizer requirements in his tanks. I'm tempted to use iron gluconate and potassium gluconate supplements as "root" tabs and see where that goes.

in terms of roots clogging up the filter, I have moved around some pretty good root balls out of the undergravel filter without too much fuss. as plant roots prefer to have oxygen near them, the "anoxic" zone of the slow moving plenum could help keep them from getting too extensive. otherwise, a mat of roots with water passing through them sounds like a pretty solid filter on its own.


I think sticking to honey gourami and foregoing the dwarf gourami would be a good idea in your tank. I kept a dwarf gourami for 2 years and he attacked anything we tried to house him with. Rummynose get fairly big bodied and could crowd up a 20l, but I don't think your filtration would run out on a group of 6 or so. White Clouds and ember tetras could give you that flash of red while occupying less real-estate.

I have been using a 4ft LED grow light from Lowes on the 45 long. It has very minimal blue spectrum and is rated for damp conditions. it was about $50. the downside is that it isn't as slim as aquarium lights. I have NICREW on everything else.


Removing the uplift tube ends up creating a "jaubert" or "monaco-style" plenum, which has been in/out of vogue with saltwater folks for around 70 years. Bob Goemans is generally responsible for bringing this style of filtration to the USA. here's his blog below.


he also has a number of books published on the method. He mentions anecdotal success for a cichlid keeper using the method.

although he advocates no uplift, he creates a plenum with a DIY method and has formalized the parameters in which it works for reefs.

1. the plenum must be less than an inch high and cover the entirety of the aquarium with no lift tube.

2. the substrate needs to be between 3-4inches.

3. "medium" grained sands/aragonite.

4. a modest amount of live rock.

I think Novak's UG filter modification makes the slow moving plenum a bit more accessible as you can just slap an undergravel in there and cut a tube.

oh, I just found an article on Reefs discussing their success with the UG method about 20 years ago.



Pardon the glare and algae on these photos. the ten gallon has 4 pygmy cories and 8 Celestial Pearl Danios who really didn't care to get into the picture. and the 45 long has 18 white clouds, 8 cherry barbs, and 9 bronze corydoras. I'm sure the plants are helping, but the 45 long crashed with 5 cherry barbs and 2 corydoras a few months back.1798548263_IMG_20210510_1506501982.jpg.118d803b7f0fbc1f420851a09f929371.jpg1517979957_IMG_20210510_1506387202.jpg.0fcc984fded57717a6d422ae5b0b58ac.jpg


Happy fishkeeping and Good Luck!

  • Thanks 1
Link to comment
Share on other sites

I appreciate your detailed response.  

Did you use sand in any of your other tanks with the plenum?   When I was worried about clogging, it was the concern of debris clogging up the weed/landscape fabric, which the latter keeps the sand from going through the UGF plates.  I was thinking of keeping the fabric between the baked clay and the sand.  But I may need to keep it above the UFG plates directly.  I just didnt want the sand to be mixed in with the clay in case I want to tear down and save the sand for later.

What did you use for iron initially?   

What I understood is the iron helps to form the bacteria needed, but once it's established, no need for the iron source.  Or maybe I misunderstood.

I appreciate the input on the stock.  I've seen dwarfs inside a 20, but not sure if he put one male with a bunch of females.  I guess I can pass on rummy nose for now.  I just love the way they school.   I do like Embers.  I've considered adding a small school to my 10g along with its lone occupant (a betta).  But right now that tank is doing well.  I think it's mainly due to just having one fish, so I may just keep it that way.  Besides, I think he's gotten used to his territory.

Link to comment
Share on other sites

I did not set up any with sand specifically, however i used some 2 year old carib sea floramax and some kitty litter straight on the UG filter. I can peek underneath the ten gallons and a little bit of the sand/fine particles made their way down, but it's very minimal and i'm not too concerned with the residue.

The saltwater folks intentionally use sand,  but they use a fiberglass mesh for window/door screens on top of their custom plenums. it's not a super fine screen, but it's just right to prevent the infiltration of sands. I used landscape fabric on the edge of the UG filter to keep gravel out. It's the same type of UG that Novak set up in his new SGA aquarium.  I think if you were to go with sand, I would follow the procedure that the saltwater folks go with, but go ahead and add the truncated uplift tube. They point out that an UG filter isn't "open" enough for sand to work and has the potential for clogging. then again, they're writing in reference to their specific context of the "jaubert" method.

experimenting is part of the fun!

I used Ironite as the starter, but I do not recommend it as I saw a gardening topic stating that it has higher levels of arsenic present than other ferts. it also contains ammonium nitrate, which can help get the cycle moving, but then you have to wait to add fish. I only used a small amount when i started. maybe a a few tablespoons in the 45 and a tablespoon for the 10s.


It is strange how laterite has sort of vanished this year. it's primarily mined in india, so the pandemic may have an impact there. High Quality Akadama soil (a highly sought after ingredient in bonsai soils) is said to perform similarly. Flourite Red is supposed to work as well. I will note that the safe-t-sorb does have some iron in it. However, i believe it is locked into the baked clay as iron oxide, which needs specific bacteria to "mine" and make bioavailable. To what extent these bacteria are present in our aquariums, I have absolutely no clue.

you could soak the baked clay substrate of your choice in a solution of iron and likely give the bacteria a good jumpstart from what I have ve come to understand about this process. I'm guessing a regular standard nail could accomplish something similar  as this study (https://www.tandfonline.com/doi/abs/10.1080/19443994.2012.708204) suggests for wastewater treatment.

Iron and trace elements help facilitate the process for denitrification. https://www.sciencedirect.com/science/article/abs/pii/S0043135402003834

While our plenums set up with baked clay are not as sophisticated as a large scale reactor in public aquaria or activated sludge plant processing municipal waste, the concept should carry over if we get the right conditions we are looking for. I think this is why novak has a dash of flourish iron hooked up to his SGA aquarium auto-fill (also the plants like it)


Bettas sure are pretty fish. Glad you've found a routine that works for you and your betta.

Otos are voracious algae eaters and i believe Aquarium Co-op has changed their recommendation for algae eaters away from otos and towards hillstream loachs for their easier terms of care.

Corydoras are absolutely amazing fish and the pygmies are unbelievably cute. We ordered some pygmies from aquahuna and are learning that they need to be kept warm at 72 degrees. hopefully they can get used to cooler temps with breeding/gradual changes.

thanks for the cheer! Happy fishkeeping!


  • Thanks 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...