DIY : Continuous Gravel Vacuum

I try to have enough bio-diversity in an aquarium so it becomes as self-sufficient as possible, and then whatever is left I'll either automate, such as timers for feeding and lights, or I'll incorporate gadgets to reduce my workload. This page documents 2 gadgets which I use together, but they can be used individually.

The first part is an apparatus which allows for a continuously operating gravel vacuum. The canister filter used for trapping the detritus, is connected to some valves which allow the debris to be quickly & conveniently backwashed.

Continuous Vacuum

I'll start with the gravel vacuum, but more properly, it's not actually vacuuming the gravel. It's a relocation of a filter's intake to the front of the aquarium, to the lowest level of the aquarium's substrate. The conventional intake strainer is replaced by UGF (undergravel filter) plates. However, while this uses the components of a UGF, it does not work like a UGF because the debris is not held in the substrate, and is 'vacuumed' up and carried to a waiting filter.

There are 2 tricks to making this work effectively. First, the stones above the UGF plates must be of a large enough diameter, that all types of detritus will easily flow past them. Secondly the UGF plates should be at a low point in the tank, and in a cleared area free of significant obstructions, so that any debris rolling along the bottom will settle there.

Cover the UGF plates with something like river pebbles (see Figure 1 below), and then fill the rest of the aquarium with regular substrate. Because of the height of the plates (1"), and the necessity to slope away upwards, the depth of the substrate might be several inches by the time the back of the aquarium is reached. For heavily planted tanks, this may be of no consequence, as this depth can be desirable. However, if undesirable, sheets of styrofoam can be used as filler (as shown in the illustration). This allows a much smaller amount of substrate to still achieve the sloped look which is desirable for the vacuum's operation.

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The styrofoam can be held down by siliconing it to the tank bottom, or by placing stones over it. Either method has pros and cons. Siliconing requires the right adhesive, a very dry tank, several days for curing, and is somewhat permanent (laborious to remove). If using heavy stones, they are best added (or removed) when there is no water (or very little) in the tank. When the tank is full, you need to remember this extra function that the stones are providing. Removing a heavy pivotal stone from underwater for cleaning, might result in the styrofoam and substrate rising up. This allows some substrate to flow under the styrofoam, preventing a proper return fit. For any tank which uses a lot of rockwork, this is not a big concern. For reference, a cubic foot of your average expanded polystyrene has a buoyancy of approximately 60 lbs. Accordingly, a square foot of 1" thick styrofoam requires 5 lbs to cancel its buoyancy. Also, your substrate adds to whatever weight your rockwork is providing. With heavy rockwork, it is recommended to use a sheet of styrofoam underneath anyway.

The connector to the UGF plate (to attach the UGF riser pipe) is not always ideally located and needs to be disguised, so some thought has to go into where to place it. If there is a grill under the connector, a hole can be broken through, once the connector's location has been finalized. A 90 degree elbow is used instead of a connector (or to replace the riser). Sometimes the parts from the UGF riser can be used for this purpose, otherwise a trip to your local plumbing or home renovation centre is needed. At the store, check the nylon fittings, ABC fittings and the components they carry to build underground water sprinklers. Between these three, I've almost always found what I needed.

Use flexible hose, tubing or solid tubes to get the vacuum intake over to the tank wall where you can turn 90 degrees upwards to connect to the filter's intake. If using a powerfilter, then you only need to connect the pipes together. If using a canister, ensure all hose connections are securely fastened. Use stainless steel hose clamps underwater. Regular hose clamps can be used outside the aquarium. An unfortunate characteristic of canister filters is that a leak can drain the tank of all the water above the filter's intake, and the intake is under the gravel in this design. I've read that making a small hole in your canister hose below the water line will cause an air lock, preventing the aquarium from completely draining, but I haven't been ambitious enough to try it yet.

A few well placed stones will cover the horizontal section of the intake pipe. It's preferable to offset any significant structure from a tank's mid-point. If the pipe will be indistinguishably buried under rockwork which spans the entire tank, then it makes no difference. If you will have a pile of rocks only to hide this pipe, then consider moving the pipe so that it is just to the side of the tank's mid-point, and/or have the pipe run diagonally towards the back. Midpoint and/or perpendicular objects tend to draw the eye, so anything offset and/or diagonal will be much easier to disguise.

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Referring to Figure 2 below, a conventional canister filter is used with a shut-off valve in the outflow (flow returning to the tank), and two shut-valves and a T-connector in the intake. The picture explains the usual sequence I follow when servicing the aquarium. While in 'NORMAL FILTERING' mode, turn off the filter (I use my delay timer for this). I then put a 6 gallon pail under the hose bib and switch the valves, as shown in 'BACKWASH FILTER'. Done weekly, this keeps the filter from accumulating any detritus. This is the same principle used with a swimming pool filter, backwashing to clean the filter media. Once the water flowing into the pail clears, I then switch to the 'DRAIN TANK' valve settings, until I have removed my planned amount for water change.

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If your return is an open pipe, and you have small fish, you might want to place something at the hose to prevent fish from getting sucked in during a backwash. A notched sponge or a draped fishnet would serve this purpose. Note that this drains water from your filter's return (ie: spraybar), so do not allow the water level to drop down to the level of the spraybar, or you will start drawing air into the canister. If your spraybar or return hose is normally above the waterline, then Harry Muscle, another avid hobbyist from the newsgroups, proposed the following design to be able to still backwash using the intake path.

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The hose bib (short hose off of the T connector) can be replaced with a garden hose fitting. I had initially built it this way, so that I would drain and then fill through the same hose. This proved to be impractical as the canister filter I'd chosen, was not up to the pressures involved. If you want to add this capability, then I suggest you add one more shut-off valve, between the T-connector and the filter, isolating the filter from the water pressure going up into the tank. Also note that the water returning back in will be flowing across the tank's exposed glass bottom underneath the UGF plates. Avoid using very hot or cold water, or the glass bottom might crack.

My return shut-off valve was a standard in-line hose valve. For the inflow shut-off valves and T-connector, I chose a heavier duty model and attached the apparatus to the side of my stand, inside a cabinet, as shown in Figure 3 below. The tub under the canister filters is only to catch small spills.


Figure 3

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