Under Gravel Filtration - The Planted Tank Forum
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post #1 of 13 (permalink) Old 09-02-2020, 11:16 PM Thread Starter
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Under Gravel Filtration

Hi everyone! So I'm fairly new to keeping fish. My question is if I have under gravel filtration and a rhyzomat plus gravel on top, is the under gravel filtration still effective? I also have a MarineLand Penguin 350 I'll be using at the same time.
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post #2 of 13 (permalink) Old 09-03-2020, 01:41 AM
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If you're using a powerhead on the undergravel, it may be all you need. It depends on how small the tank is, what fishload you're stocking in it, and if you are planting in the rhyzomat.
Give us some more tank/plan info and others more experienced who keep the same type of tank may chime in.
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post #3 of 13 (permalink) Old 09-03-2020, 02:00 AM
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My advice is to not use an under-gravel filter, particularly if you have a planted tank. With a planted tank, it is best to leave the substrate alone and allow the plants to access the nutrient accumulation. Although some deep-vacuum their planted tank substrates regularly, I don’t and there is much support for not doing it in a planted tank. A light surface-only vacuum is the most that should be done, in a planted tank, and I don’t even do that. Instead I ensure a good sweep of the surface via circulation. There are situations that do require deep cleaning when certain problems appear.

Now, for non-planted tanks, I also suggest not using an under-gravel filter. I used one for decades, in addition to a HOB filter. The concept that organics and other detritus will eventually breakdown and flow through the substrate and back into the water column is only partially true. There is a sludge build-up that occurs in all filters and, left uncleaned, becomes quite heavy. This is easy to remove from external filters, but not from under-gravel filters. The sludge simply builds and builds in the open area at the very bottom of the tank (under the under-gravel filter) and cannot be easily removed. Depending upon the type of plants you may add/have, the roots can grow down below the filter and then block flow where it should be flowing freely. I had an Amazon Sword, once, whose roots covered about 50% of the floor of my 29-gal. This sludge then continues to throw off organics, although much of the sludge does become inert, eventually.
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post #4 of 13 (permalink) Old 09-03-2020, 04:32 PM
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Go ahead and use the UGF more as a plenum than a filter (with reduced flow) and it will be great. Plenums in the FW aquarium

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Last edited by AbbeysDad; 09-03-2020 at 06:03 PM. Reason: update
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post #5 of 13 (permalink) Old 09-04-2020, 01:02 AM
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Go ahead and use the UGF more as a plenum than a filter (with reduced flow) and it will be great. Plenums in the FW aquarium
This article suggests an interesting theory, but the author didn't actually test it. He was only sharing something he found elsewhere and even that source seems to only "suggest" what might happen. Personally, I doubt that much, if any, anaerobic bacteria develops (to reduce nitrates) in an UGF because the water movement is unlikely to be slow enough and, I would think, any water moving completely through the substrate is going to be oxygenated. Additionally, you are supposed to deep-vacuum regularly, to keep flow going.

Anecdotally, my experience was that nitrates climbed as a function of the sludge buildup under the UGF. I was able to remove about half that sludge by inserting a flexible tube down the flow tubes and suck out some of it (a difficult process). After doing this, nitrates would drop, but we are only talking about 5-10ppm. As I mentioned, above, I found that by adding a HOB, I was able to reduce sludge buildup, somewhat, and keep nitrates lower but, perhaps, the HOB was simply adding more stabilization to the overall filtering need. I finally bit the bullet and pulled the UGF out. This further reduced nitrates. However, I will admit to habitually overfeeding my overstocked tanks and, as you know, this can contribute to sludge problems.
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post #6 of 13 (permalink) Old 09-04-2020, 03:39 AM
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Quote:
Originally Posted by Deanna View Post
This article suggests an interesting theory, but the author didn't actually test it. He was only sharing something he found elsewhere and even that source seems to only "suggest" what might happen. Personally, I doubt that much, if any, anaerobic bacteria develops (to reduce nitrates) in an UGF because the water movement is unlikely to be slow enough and, I would think, any water moving completely through the substrate is going to be oxygenated. Additionally, you are supposed to deep-vacuum regularly, to keep flow going.

Anecdotally, my experience was that nitrates climbed as a function of the sludge buildup under the UGF. I was able to remove about half that sludge by inserting a flexible tube down the flow tubes and suck out some of it (a difficult process). After doing this, nitrates would drop, but we are only talking about 5-10ppm. As I mentioned, above, I found that by adding a HOB, I was able to reduce sludge buildup, somewhat, and keep nitrates lower but, perhaps, the HOB was simply adding more stabilization to the overall filtering need. I finally bit the bullet and pulled the UGF out. This further reduced nitrates. However, I will admit to habitually overfeeding my overstocked tanks and, as you know, this can contribute to sludge problems.
I'm not sure you looked closely enough and it would seem you didn't bother with the embedded videos. This is not unlike deep sand in SW aquariums.


The objective with a very slow flow rate (of a gallon or two per DAY) is to create an anoxic environment, and not an anaerobic one. With such a low flow rate, deep vacuuming is not required or desired. This is not unlike Dr. Novak's research in anoxic biocenosis clarification baskets, just fits neatly inside the aquarium. Also, he claims to have systems running this way for up to 10 years, with 6 months between partial water changes and 5-10ppm nitrates consistently (although it's lightly stocked and has plants).

So maybe it's nothing, or maybe it's really something!


BTW, I guess you missed that I AM the author of the article reporting the research of Dr. Kevin Novak Ph.D. As I mentioned in the article, I have been testing anoxic biocenosis clarification baskets, but yes, I have yet to test using the UGF plates as a plenum.

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post #7 of 13 (permalink) Old 09-04-2020, 06:26 AM
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... an anoxic environment, and not an anaerobic one
An anaerobic and an anoxic environment are the same thing... anaerobic respiration takes place in an anoxic environment. What is the distinction you're referring to?


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post #8 of 13 (permalink) Old 09-04-2020, 12:36 PM
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An anaerobic and an anoxic environment are the same thing... anaerobic respiration takes place in an anoxic environment. What is the distinction you're referring to?

In any somewhat deep substrate there are three layers, aerobic, anoxic, and anaerobic. Lots of oxygen in the aerobic layer, little but some O2 in the anoxic layer, no O2 in the anaerobic layer. It's my understanding that different bacteria flourish in the different layers. We are all aware of aerobic bacteria nitrosomonas and nitrospira that convert ammonia to nitrites and nitrites to nitrates, but it's anoxic or anaerobic bacteria that converts nitrates into N2 gas. Dr. Novak's research seems to conclude that anoxic bacterium does a better job than anaerobic, without producing foul odors and hydrogen sulfide.
I don't profess to be an expert on this, merely reporting some interesting research information. But one has to ask...if we can have live rock and deep sand in SW to lower nitrates, why not something for FW to better complete the nitrogen cycle?
Now I've always been one to 'preach' the merits of routine partial water changes - partial water changes, lowering aquarium nitrates. But if there's a method to better maintain water quality, why not leverage it?

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post #9 of 13 (permalink) Old 09-04-2020, 01:08 PM
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Originally Posted by AbbeysDad View Post
I'm not sure you looked closely enough and it would seem you didn't bother with the embedded videos. This is not unlike deep sand in SW aquariums.


The objective with a very slow flow rate (of a gallon or two per DAY) is to create an anoxic environment, and not an anaerobic one. With such a low flow rate, deep vacuuming is not required or desired. This is not unlike Dr. Novak's research in anoxic biocenosis clarification baskets, just fits neatly inside the aquarium. Also, he claims to have systems running this way for up to 10 years, with 6 months between partial water changes and 5-10ppm nitrates consistently (although it's lightly stocked and has plants).

So maybe it's nothing, or maybe it's really something!


BTW, I guess you missed that I AM the author of the article reporting the research of Dr. Kevin Novak Ph.D. As I mentioned in the article, I have been testing anoxic biocenosis clarification baskets, but yes, I have yet to test using the UGF plates as a plenum.
I did take the time to watch the videos, but didn’t comment on them, specifically. I’ve encountered his videos, on other subjects, before and have been very skeptical of his approaches. He definitely is thinking ‘outside the box’, though.

I would be more convinced if your experiments with it proved to deliver the goods. So, if you would report on your results, I would very much appreciate it. I do realize that it can take many months to establish what is, essentially, a denitrification factory, so I won’t expect anything soon.

Incidentally, if any of you are interested in some denitrification discussions, you might find these links interesting (pay particular attention to Phil Edward's (both @PEdwards and @Phil Edwards) postings.

https://www.plantedtank.net/forums/1...ol-dosing.html

https://www.plantedtank.net/forums/1...-products.html

Last edited by Deanna; 09-04-2020 at 01:28 PM. Reason: Add
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post #10 of 13 (permalink) Old 09-04-2020, 03:08 PM
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Iím not getting into the debate on the scientific merit of UGF but want to point out that canister filter, HOBs or sump system are essentially external UGF. Over time, all filters including UGF will get clogged up and no longer function as intended and cleaning up an external filter is much easier and less messy than cleaning a UGF. The last time I had an UGF was when I was a kid keeping small fish in a 10 gal. Every 6 months to a year I had to break up the system, take all fish and plants out into a bucket so as to rinse the system to start over. Itís not so bad with a small tank, few plants, and light fish load. Its proportionally more messy to maintain an UGF with bigger tank, higher plant mass and fish load. With higher bioload, such as a cichlid tank, the UGF will get clogged up at no time and maintenance will be a nightmare.
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post #11 of 13 (permalink) Old 09-04-2020, 04:27 PM
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I love reading the Novak stuff because it makes me want to refer to myself as Dr Bunsen Honeydew, PhD.

To continue the sidebar, why would I want an anoxic bed to convert nitrates to N2? I already have to put nitrate in every week as it is.
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post #12 of 13 (permalink) Old 09-04-2020, 04:30 PM
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Actually, the conventional UGF is a great bio-filter with acres of surface area for BB...more than bio-media in any filter. But it does require routine gravel vacuuming to get the crud out, or it turns into a nitrate factory. And @Tiger15 is correct, it's increasingly difficult in a larger tank, especially if/when planted. There's also an increased negative if larger gravel is used as too much uneaten food and waste gets deep under too quickly. The reverse flow UGF was an improvement.
But this plenum idea is very different from the conventional use because the controlled flow is so very low as to not aggressively pull detritus down under. Dr. Novak even shows a method to use sand by placing landscape fabric between the UGF plates and the sand so no sand or yuk gets down under the plates. I'm thinking pool filter sand would be great for this as it has the perfect particle size to allow permeability without letting crud get down under the surface.
So if nothing else, the 1-2 gallons per day flow through a sand bed should make for an effective bio-filter, even if nitrates weren't converted...and if they were - wow.

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post #13 of 13 (permalink) Old 09-04-2020, 06:07 PM
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Originally Posted by AbbeysDad View Post
In any somewhat deep substrate there are three layers, aerobic, anoxic, and anaerobic.
Are you considering the anoxic zone one where there is diminished oxygen but it is not completely depleted? A better word for that would be hypoxic. Anoxic means NO oxygen in the water column. Sediment microbial communities definitely have a gradient from aerobic to anaerobic dominated but the term "anoxic" very specifically means somewhere there is no oxygen, which means all microbial respiration in an anoxic environment would be anaerobic. A more accurate way to describe this transition would be from an oxic environment, to hypoxic, to anoxic. Mixing up cellular respiration processes with dissolved oxygen descriptions is just a little confusing.


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