Undergravel filter

[western44]

Hi all, i was in a lfs not my usual lfs and i noticed they had undergravel filters for sale, something that i have'nt seen for many years.
It got me wondering as i have a spare tank, would it be possible to run an undergravel filter with a small external filter, if so how would
you do it. Thanks in advance.

 

[_Maq_]

Tried in early 2000s with a powerhead on the uplift tube, but plants didn't like it. And I got used to the silent running so ditched the UG filter. If only there was a truly silent air pump !

What you say suggests that UG filter worked well only when the water flow was very modest. Is that so?

 

[_Maq_]

I am very distrustful of stagnant substrates, they may be natural but when wading through them the pong that comes up is very indicative of low oxygen.

Bad smell is not an indication of low oxygen. Of course, bad smell (hydrogen sulfide) develops only in anoxic conditions, but it does not mean that whenever conditions are anoxic, hydrogen sulfide develops (in noticeable amount).
As I understand it (and I've read quite a lot of literature about it) the substrate is always suboxic/anoxic, yet only if there's abundant organic matter present processes resulting in foul smell occur. In other words, if you keep organics low in the water column and the uppermost layer of the substrate (=keeping organic pollution low and oxygen high), then lower layers remain oxygen-free but bad smell hardly occurs.
This is the reason for which I'm wary of active/nutrient-rich substrates.

 

[Polly]

What you say suggests that UG filter worked well only when the water flow was very modest. Is that so?

Possibly, but thinking about the undergravel plate I used, I think it was inadequate. It was like the Supa under gravel plate https://www.amazon.co.uk/Supa-Under-Gravel-Aquarium-Filter/dp/B003J2ULO6/ref=asc_df_B003J2ULO6/?
The slots were really tiny and clogged easily.
Have just set up my aquarium with the more open undergravel plates which I'd kept (attics are great !) with the same powerhead, but it's turning over only 1.5x tank volume. There's flow throughout the tank, but it's very gentle.
Gravel is a layer of mixed pea 3-8mm and a layer of 3-5mm on top. Azalea root, pebbles and Planted. Want to change out some of the plants and add some Blyxa to be more in keeping with the fish
As time goes on the plan is to add botanicals - leaves, pods etc and cover the substrate.

If I feel that the powerhead is too much, I can easily swap it for an air pump

 

[JnSchutz]

Hello hello

This thread is great, and since I just set up a UGF I decided to join, as to add more info.

I set up using the same fabric method as @Oldguy did:

I run a UG in my planted tank. I used garden weed suppression fabric on top of the plates and then ordinary 'fine' gravel substrate on top. The weed suppression fabric is surprisingly porous and water just flows through it.

But I use a geo fabric, that is used around street drainage pipes, that allows water flow out of the cement pipes through the soil, but not the dirt.
Also I didn't put plates all over the blue print, just one stripe 5cm from the aquarium front glass as shown in the picture:

I have two uplifting tubes connected in the center to one power head.
To have a better distribution of the flow, I placed each uplift near towards the center of the plate:
If you look carefully in the picture you will notice two small squares in each endpoint plates, they are pointing towards the aquarium center. There are 7 plates in total.
I know the ones towards the middle will have less water push, but this way I find to be a little bit more consistent.

But I do not plan on vac cleaning the substrate, I want to see how long it will go without any intervention, of course I will check the power head.

I often consider this option of a reversed flow undergravel filter for my imaginary future tanks, but I worry about not having an anoxic region in the substrate. How would it impact micro elements availability to plants? How would it impact root function?

I was worried about this too, I don't know the exact rock science behind anoxic layers in aquarium, I'm a slow learner.
But for some reason I did want a anoxic part in my aquarium, this is why there is plate only in a area of 84x12 (cm) towards the front. My aquarium blueprint is 100x40, so only 1/4 of the aquarium base has Under Gravel plates.

LMuhlen, you should try it and maybe start a new trend!

So why not get into this trend and check how it goes?
I decided for a mix of UGF with anoxic areas after watching some YT videos of nice planted tanks, but was the comment section that drove me into trying something like this, because I couldn't find any video or tutorial on how to make it, although I know someone has already tried it.

More info about the set up here: Journal on my new 200L low tech with Under Gravel Filter


At the back of my aquarium there is a slope, that is almos 20 cm (8 in) in height, so I think that there will be an anoxic layer.

But that's the point. We do need suboxic and anoxic zones in the substrate.

Hey @_Maq_ , could you share a little bit more info about this?

That's the prerequisite that plants can pump enough oxygen into their roots, and that oxygen-depleted zone does not reach the uppermost layer of the substrate. Everything below that layer should remain suboxic / anoxic. The richest and most important microbial processes take place at the oxic-suboxic interface, and these spots should not be too far from plants' roots. If the substrate remains oxidized, acquisition of some nutrients, esp. phosphorus and transition metals, is compromised.

I have learned that in anoxic zones there would be another kind of bacteria that would do the reverse of the nitrifying bacteria, they would convert the Nitrates into Nitrites and then to ammonia somehow (usually I invert the order between Nitrate and Nitrite, I'm dyslexic, and it is really difficult for me to tell them apart, sorry if I messed it up).
But, this bacteria that works "backwards" would be beneficial for supplying plants with ammonia.

Yet, I found almost no root system deep down in my old tank when I dismantled it, actually I think I found none, but the soil was really compacted and heavy. I don't know the dynamics. More info needed

About the water flow, turnover:

The slots were really tiny and clogged easily.
Have just set up my aquarium with the more open undergravel plates which I'd kept (attics are great !) with the same powerhead, but it's turning over only 1.5x tank volume.

Now I'm concerned: my plates have tiny slots, covered with a geo fabric:

Each slot is 20 mm x 1 mm (3/4 of a inch by 1/32 of an inch - I have no idea if I read it right)

There's flow throughout the tank, but it's very gentle.

My power head has a turnover of 600L/h, divided by two uplifts. The ration for the aquarium total volume is about 3 times, but the water volume above the substrate is about 120L so the ratio of turnover is around 5x. Of course there is resistance from the substrate the geo fabric etc etc etc.

If I feel that the powerhead is too much, I can easily swap it for an air pump

I wish we could add short videos to show the water turbulence. When I set it up there was more water movement than now.

@Polly, can you share your thoughts on why a lower flow rate would be better for a UGF?

Cheers
Jonni

 

[JnSchutz]

Hello hello.

So the slots were tiny and the geo fabric help it to become clogged.

As I have written in my Journal on my new 200L low tech with Under Gravel Filter, the UGF was running slower and slower, more like a plenum, the set up is only a month old by now.

I think I will have to do some major maintenance: remove the substrate above the plates, remove the fabric and replace the plates for ones that have bigger slots.

Cheers
Jonni