Undergravel filter : Am I crazy? - The Planted Tank Forum
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post #1 of 6 (permalink) Old 09-07-2004, 09:41 PM Thread Starter
Algae Grower
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Location: Norfolk, England
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Cool Undergravel filter : Am I crazy?

Below is my plan for deploying a UGF in a plant & fish (cardinals only) tank.

Have you ever tried something like this? Please let me know what you think of the plan - good or bad!

Apart from radiantly healthy plants and fish, my goals with this are; low-ish maintenance, very long term sustainability, no messy, expensive or layered substrates, low turbulance, large (stable) bio filter volume, "natural" plant fertilisation, no 100% dead areas, no heater cables.


An external canister filter reverse-feeds an UGF.

A fine (20um) filter sheet is placed beneath the area(s) to be planted (about 75% of area in my plan).

75mm - 100mm of fine inert gravel (< 2mm) is layered on top.

Thats it!


The point of the fine filter sheet is to ensure that the flow in rooted areas is fairly low, encouraging further natural "clogging" whilst allowing a very small residual flow (i.e. no totally dead zones or heater cables!).

The cut out(s) in the filter sheet should concentrate the return flow trough the unplanted floor area(s), reducing the clogging there. The unplanted floor area(s) act as high volume filter and low turbulance return path and will be "hoovered" regularly if necessary.

This setup would of course only suit aquascapes where leaving some of the floor area unplanted is acceptable or desirable.

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post #2 of 6 (permalink) Old 09-07-2004, 10:44 PM
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No clue. I abandon'd UGF's due to their inferior filtration method. Canisters and lots of plants is my technique.

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post #3 of 6 (permalink) Old 09-08-2004, 12:09 AM
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Ianice, welcome to the Planted Tank!

It's an interesting theory which hasn't proven to be long-term stable. Several issues:

The slow flow through the substrate is still too fast, and the oxygen-rich water makes trace elements unavailable to plant roots. Not much of a natural fertilization. Sure, you could reduce the flow to almost nil, but the many plant roots will further block the little flow and finally there won't be any, so why go through all the troubles?

Roots find their way down into the UGF cavity, clogging it up over time. Again, it works for the unplanted area, but what's the point? Fishies and plants don't mind a little turbulence (water movement), and in a planted tank, biofiltration isn't that much of an issue anyway.

For root feeders, adding some kind of fertilizer tabs to their proximity is almost necessary when using gravel. The reverse UGF will slowly move that into the water column. There isn't much control in terms of where the actual flow occurs, but for sure it ends up in the water instead of feeding the roots.

The normal tendency of mulm/fish poop to disappear into the gravel will be reversed by the reverse UGF, instead of disappearing, it will collect on the surface (I think). A big sponge in a canister filter has a better holding capacity and is easier to clean than an area of gravel in your tank.

You might end up having radiantly healthy plants either way, but with the UGF, you actually hear a little time bomb ticking... a place that slowly fills up with yucky muck, although... maybe you could reverse the flow and suck out the muck once in a while... Maybe you should just try it!
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post #4 of 6 (permalink) Old 09-10-2004, 05:06 PM Thread Starter
Algae Grower
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Red face

Thanks for your comments.

I have almost abandoned the UGF plan already

How does a "canister-only" system run long term if there are a few fish around?

I only intend to have 20 or so cardinals in a 48 x 15 x 18 tank but coming from a "fishy" background I am slightly nervous about running without large bio-active medium somewhere in the system . Actually the truth is I am a bit lazy and in a hard water area so I dont want to do too much water changeing.

I presume you wouldn't recommend areation of any sort if you are adding C02?

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post #5 of 6 (permalink) Old 09-10-2004, 06:19 PM
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you would be wasting your time using an air pump. all the agitation from the bubbles would cause you to lose most or all of the co2. besides, if you have enough plants they should produce enough oxygen..

75 gal, Schultz aquatic soil substrate. Filstar XP2 and a H.O.T. Magnum canister filter, 20# Pressurized Co2, Coralife 4x65 watt pc lighting.

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post #6 of 6 (permalink) Old 09-10-2004, 10:12 PM
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20 cardinals in a 50gal or so planted tank isn't much of a bioload. Unless there is a couple of plecos lurking somewhere

Canister filters have a comparatively large surface for beneficial bacteria, and if you are careful when cleaning the filter the will not be harmed, but again, in a planted tank biofiltration is pretty much done by the plants.

The problem with being lazy is that if you have a planted tank, you need to feed the plants, and the fertilizer that you throw into the tank somewhat messes up water chemistry, and therefore most of us end up with rather large weekly water changes. If that isn't your thing, you might shoot for the low-maintenance method, where you use only around 1.5Watts/gal light, little or no CO2, and undemanding plants which grow slowly and thrive mostly off whatever the fishes metabolism (and decaying plants, leftover fish food...) produces.
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