Building a Hamburger Matten Filter (HMF) for an Aquarium

I had read a lot about the Hamburger Matten Filter - from hereon referred to as HMF. The HMF is said to:

- Be a cheap filter to install
- Create a (very) large filtering surface for (good) filtering bacteria to do their work and therefore function better than the average internal filter
- Give you room for CO2 and Heating to be hidden in the filter
- Not take up room outside the tank (one of my favorites)
- Give opportunity for experimenting with aesthetics
- Be big fun in combination with shrimps as the low water flow and filter bacteria give them plenty of surface to graze

Some of the things I personally found to be a downside were:
- In a typical HMF, there is just one filter chamber. In typical external canister filters, there are 2 or 3 chambers
- You have to build it yourself to create an optimal filter. That means having to glue inside your tank and thereby devaluing it a bit
- There is no easy way to change the filtermat, even if it only needs to be changed once a year

Given the above I decided to give this DIY-project a GO. I have carefully documented all my findings on my blog: http://hmf-shrimptank.blogspot.com, of which this instructable is an extract.

As can be seen from the plan, there is a second chamber behind the filter-mat that contains ceramic rings that are normally found in cannister filters. The third room, the inner-most room of the quarter-circle design, contains the pump and can contain other equipment or additional filter materials. As can be seen I've modeled overflows to the final chamber.

It was my specific intention to build the filter in a 'closed' format, i.e. the chambers are closed and the filter can be placed in the corner of any tank without having to glue anything. The water pressure and weight of the soil should, in combination with the enlarged footplate, keep the filter in place.

I also included a curved 'barrier'  for the soil to be put up against. This doesn't touch the filter, So I can exchange the mat without having to move the soil.

Using the information on janrigter.nl, it was easy to calculate if the filter I was about to build would obey the laws of building a good HMF:

a 10cm radius, and a height of 30cm (the height of the tank), would provide a filtering surface of h x w = 30 x w = 30 x (1/4 x outline) = 30 x (1/4 x Pi x radius) = 150 x Pi ~ 471 cm2
the pump capacity of the pump I ordered was 250 l/h. That brings the flow-rate to (250 x 60 x 1000)/471 = 8,87 cm/min. This is right about what it should be  -- again I used the formula on janrigter.nl
In fact: I used the other formula for Q to find the minimum and maximum pump capacity that would drive me to the minimum and maximum flow-rate described. That brought me to a pump capacity varying between 140 and 340 l/h. I settled in the middle.

Filter material (I used filter mat for pond-filters bought at a gardening center -- Intratuin)
The mat measures 120 x 60 x 2 cm, which is plenty of surface for the filter I designed

Lycra (I used 2mm thick material bought at the local DIY store)
The glas measures 120 x 60 x 0.2 cm. In hindsight, Plexiglas would be the better choice as it is better to be used in combination with adhesives and withstands heat better.

Tubing (1 meter at the aquariumstore (Heems))
90 degree angles for tubing (2) (Heems as well)

Two suction cups to fix the tubing to the side of the tank (Heems as well)

Silicone Kit for use in aquaria (Finally found it at the hardware store: Gamma)
Shrimps are sensitive to chemicals, don't use regular kits!

Two cable chutes I had lying around will be used to clamp/fix the mat
I only use the part normally fixed to the wall. It is exactly fit to push the mat into

All parts are in, ready for assembly. Take your time if you're planning for an activity like this; it's not over and done with in a rush. The end result is nicer if you plan carefully and take the time to work with the materials.

First I drew out the acrylic parts on the acrylic. It has got protective foil attached. Leave it on there and you can use it to draw your lines with a normal pen. I then attached painting-tape to prevent the glass from breaking while cutting/sawing it in shape. I decided to go for the latter with an old, small-toothed saw. 

The pictures show the upstanding sides of the filter. I also created two squares to form the base. The two are to be glued on top of each other to form a solid base. The lower plate is slightly smaller, to allow for the silicone glue in the sides of the tank to stay intact.

I then used sanding paper to make the edges nice and even. I also created the overflows in the smallest of the upstanding parts. Note that you need to cut out the overflows quite deep, as otherwise the waterlevel will need to be fairly high for the filter to start working!!! (one of my pitfalls...)

I removed the protective foil and used a 'creme-brulee torch' we had lying around, the edge of an old table and a piece of spare wood to bend the sides in a 90 degree angle (along the table, flattened with the wood as the plastic becomes hot). The end result, already in combination with the base and the pump (for illustration purposes) is shown on the right:

As mentioned I used special purpose silicone kit to glue the sides and the bases together. This is a slow process and an ugly result - unless you're really good with this stuff. For future attempts I would prefer to spend a little more and buy 'welding-liquids'. These melt the plastic locally and 'weld' it together. The result is much cleaner and stronger.

I then cut the old cable guides to fit and glued them on the sides to hold the mat. I also used a spare piece of plastic to bend in form of the mat that is intended to keep the soil away from the filtermat for easier cleaning/removing. I then cut the mat in shape (calculations make this easy) and inserted it into the cable guides. A last photo before testing is shown in the pictures below:

The final test is to put the filter into the tank. Luckily I had done my calculations correctly and the filter exactly matches the tank. See the picture.

With the filter finished, it is time for the finishing touches: Filter Materials, Tubing and Testing.

Filter Materials:
As mentioned I want to use ceramic rings in the middle section of the filter. I do want to change/wash them every once in a while so easy removal is key. I used a new (mind the detergents in used ones) bag that we normally use to wash delicate laundry. I put in in the filter and slowly filled up the bag with rings. I cut off the remaining piece of the bag, as it was too large to fit in the filter completely. 

Tubing:
With two 90 degree corner pieces and some standard tubing (that I knew would fit the pump!) I created the tubing upward out of the innermost filterchamber and via a 90 degree turn to a horizontal piece. The last 90 degree turn then guides the water to the outflow. I created the outflow from a piece of PVC that I had lying around. I shopped the internet beforehand, but only found expensive outflows for either original filters or lily pipes. The latter is nicer, but expensive. I simply cut the pipe, poured hot water over it, bend it in a (roughly) 110 degree corner and flattened it. I then attached it to the tubing. The end result is shown in the pictures.

Note that I bent two small pieces of plastic to form attachment clips of the filter to the tank. Easy does it!

Testing:
I then filled up the tank with soil in order for the filter to remain in place and water. I tested the filter and checked it regularly. As you become used to it not leaking or malfunctioning, you automatically check less frequently. I checked water quality using a 7-test strip and kept this running for about two weeks.

Is everything fine??? Only now has the time come to put in some plants and/or fish/shrimps. Do not do this earlier, as chemicals may still be present in the tank!!!