To Plenum or not to Plenum..that is the question.

[Stan510]

The hot topic right now is Co-op and Kevin Novak over the need for a plenum filter that is based as I understand it on waste water recycling. Basically it removes ammonia that is sky high and reeking in polluted water. Now,I've never made one because my aquariums never seem to have ammonia problem as long as I don't overstock and over feed. As far as deep sand beds? Again..in wastewater plants that is useful. In aquariums any bed over 3" deep to me is wasted as our aquarium plants don't have ( usually!) the powerful root systems of plants used to filter toxic water when it leaves the water filtration plants. Cattails and the like can plow through pure muck. In aquariums a sand bed of 4" will just smother the roots. That's what I've seen. Now dirt beds are different. Deeper might work if you are using compost and not true clay dirt. Even then,it will eventually evaporate..but that's another topic.
Plenum filters are something you might run in a sump to polish the water I suppose. Its like so many other ways to do that..from plastic shelves filled with lava rock to some floating media filter that jiggles in front of your eyes. Reverse flow undergravel filters are sort of a plenum. How strict you want to be is up to you.
I like to simplify my aquariums. If it only takes a little more media and less fish?..I try that-lol.

 

[AbbeysDad]

Using a Plenum in a Freshwater Aquarium

In some ways the plenum takes the undergravel filter back to it's roots by ever so slowly moving water through the substrate. Some feel that the UGF was compromised when greater and greater flow rates were falsely presumed to improve filtration.
In theory, the plenum creates a more perfect environment for bacteria and microbes that aid in water purification. I'm not sure that it's ever really been proven...

 

[Stan510]

I should mention now that you remind me,that When I used plants over an undergravel filter back in those days- the plant roots clogged the filter. I remember water quality went down. Really,I don't see why its said to root plants in the plenum. Plants in separate pond container or in an aquarium plants in trays over the plenum- but now I'm just tossing out ideas. No proof.
I think it sounds good- and does resemble all those reef "reactor" tubes filled with crushed coral or other material,so it looks scientific..but not sure if most aquariums NEED one.
One last- reverse flow undergravel filters have made a comeback in ponds. But you need a really deep pond for those to work. So,we are talking big bucks here and you might do just as well with giant sand filters..as done in public aquariums for the last century.

 

[AbbeysDad]

Often not considered, but the substrate is a great bio-filter (see The Very Best Aquarium Filter) that 'could' be enhanced with the very slight flow through that the plenum would provide.
Bio-medias are often rated (or promoted) based on their surface area....and there is no filter media that can even come close to the surface area that the substrate provides. Additionally there are bacteria and microbes that prefer different levels of oxygen that can only be found at various levels in the deeper substrate.
Now I've experimented with Anoxic Biocenosis Clarification Baskets (and still have a small unit on my 60g display tank in the LR) but I'm simply not convinced that they are the "be all / end all" cure for nitrate elimination....or even reduction for that matter. Then again, there are others that are convinced that they work and I'm not working in lab conditions with controls and such.

 

[Stan510]

That's true. I've been telling the newbies "Sand substrates do almost nothing to help filter your water." Gravel does. When the flow of the pumps goes over a whole substrate of gravel,you can see the difference. Decades ago I tried sand. My water was never crystal clear with various fish some large. I took out the sand,put in gravel and cured!..water quality went up.
With my big tank I went sand four years ago ( back in the hobby and seeing what's popular I tried it again) and what a mistake again!. Since then I've been adding bags worth of gravel and water quality and plant growth went up. For some reason,the sand layer is lower than the gravel. They seperate.

 

[AbbeysDad]

I've been telling the newbies "Sand substrates do almost nothing to help filter your water." Gravel does. When the flow of the pumps goes over a whole substrate of gravel,you can see the difference.

We'll need to agree to disagree as I feel sand is a much better substrate than gravel because uneaten food and waste does not get down under with sand like it so easily does with gravel ... but each to his/her own,

 

[Stan510]

Sand packs down. Put a rock over sand,and when you move it days or weeks later hydrogen sulfide bubbles are released. Everybody thinks Amano planted in sand. He didn't. He used the sand for decorative effect. Plants went into his gravel grains. Those grains are far larger than sand- and black too.

Back to plenum. One positive is I haven't read or seen any reports that they go bad. No fish kills.
I think like carbon,they boost water quality but with plenum I don't think the boost is all that much unless you crowd your aquarium or have messy eaters.
That's why nobody in the hobby and profession has admitted to using one constantly. Amano ADA channel has gone over filters and additives and never once mentioned using a plenum.

 

[AbbeysDad]

Sand packs down. Put a rock over sand,and when you move it days or weeks later hydrogen sulfide bubbles are released.

Not true, it's a myth - there is nothing in sand to generate hydrogen sulfide! Hydrogen sulfide might be created if sand is stirred such that organic waste is stirred down under to decay anaerobically.
I have several tanks with 3-4" of play sand or pool filter sand and have never had any signs of negative gases.

 

[Stan510]

No the sand isnt generating per se- but in an established tank with lots of mulm that happens. I've had it happen. I've seen that in habitat too. Pick up a rock in a slow moving warm summer day stream and the muck under it burps.
Now if we are talking beach sands? Totally a no go. If the sand is good enough for the proverbial hourglass,it's too fine.
Why do you think ADA and other companies' sell power gravel for plants? And the sand is for show..making paths or for the center of the aquarium.
Like I said- sand over potting soil is different but I would advise people to use gravel over that potting soil..sand might just mix in asap.
I've only had Crypts root well in sand. All other aquarium plants struggled to push roots into sand. Why I wonder Novak says plants over a plenum. I know he has a reason...
I bought years ago a white gravel labeled "Silica sands" sold for sandblasting It was the perfect grain. I can't find it anymore.