How to set up of a Rocky coast aquarium, with a built-in background filter...
and also a little about handy modifications to the equipment, and removal of old glued-in modules!

Finished setup app. three moths after start.

A little info about the used tank, technical installations, choice of materials and decoration.

The tank to be used, is a  900 liter Akvastabil Effectline, with a black anodized aluminum frame. the stand is a matching standard aluminum construction, cut down to a height of 47cm (+ the height of the adjustment screws). The Lamp is the matching Effectlight lamp.

The tank, stand and lamp. The setup is placed on a 27 mm oiled pine tree plate

It was acquired August 2010, and was originally used as a community tank, for South American fish, as shown below.

The original setup


From planted community tank to a Rocky coast setup

Preparing the tank

In the previous setup, a Back-to-Nature module was glued in, placed in the right hand corner. I have opted for a full artificial background, so this module has to go. The module was glued to the glass, using silicone, and had to be cut free, using a hobby knife for the first couple of cuts and a salmon filet knife, which is really good at this, because of the flexible blade, for the rest. The flexible blade makes it relatively easy to keep the blade very close to the glass, leaving only a little glue. It is advisable to use extreme care, when the blade is close to the seams of the tank!

The mentioned module is clearly shown here.

Preparing the lamp

The lamp is originally equipped with armatures for 2 x double 39W T5 tubes, but was modified to hold 4 x 39W, in order to provide sufficient light for the plants in the previous setup.

The lamp with the extra armatures mounted.

This extra light is no longer needed, in fact there really is no room for it, with the projected background mounted, so the extra armatures must be removed again.

The lamp is shown on the tank, with the background mounted. As evident, the extra tubes used in the previous setup, would send a good deal of their light right down into the filter, and the rest would put way too much light on the background, detracting from the desired effect.
Mounting the background

I have decided to try out one of the highly acclaimed background filters. Everybody with any experience from using them, seems to have only positive things to say, and I got a very convincing demonstration from the dealer (Unimati in Randers) who sold Me a complete background/ filter material package.
The very handsome background, a RockZolid Papua, measuring 198x58 cm, is heavier than water (made from some kind of glass fiber, I think), so it could just be pushed in place, but since it is going to be used as a background filter, it must be glued in, to make it watertight. Full backgrounds often require that the metal bar holding the front- and back glass together, is removed, but in this 900L tank has more width than height, so it is possible to push the background into the tank lying down and subsequently raise it to upright position inside, so this was not necessary here.

A tank with the mentioned background (and two matching modules on the bottom). The image is taken from www.Unimati.biz, with full permission.

The dealers instruction for mounting (in Danish, but with excellent illustrations)

More about the background

The background was a little bit too long, so it had to be shortened by app. ½ inch. The best tool for that is an angle grinder. A jigsaw CAN be used, but the glass fiber does have a tendency to splinter, Generally speaking, it is worth considering that the background is fairly fragile, and that especially the corners may break off, if not handled carefully. Using the angle grinder is however, very simple and safe, but protective eyewear is recommended! Also some form of clothing to protect hand/arms is good, as the fine dust from the cutting contains splinters, that stings and itched for a long time, if it settles on the skin. Holes for in- and outlets are drilled and grids are glued in at the inlets, which in this case is 60 mm wide. If desired, a notch can be cut off at the top corner at the inlet-end, to create an overflow inlet. Also remember to cut the bottom corners, to avoid damaging the silicone sealants of the tank!

Outlets placed in the left side of the background, and inlets in the right. As evident in the left hand picture, I did manage to mount the background a little too low! The number of in- and outlets are determined by the number of pumps used and the throughput the filter is intended to have (in this case app. 3000 l/t.). The inlets MUST be covered by some sort of grids! The outlets are not strictly necessary, if there is room between the background and the lamp/glass cover to lead hoses over the top of, instead of through the background.

Pushing the background into place, is a pretty hairy experience, if You haven`t done it before, and doubts may easily arise, if it is even possible for the thing to fit, since it gives off sounds that have a remarkable similarity to protest cries! With patience and controlled force (just remember that it might break if pushed too hard!) it does however, usually give in, provided that Your measuring is correct. Determining how far back it should be placed is easy; just push it up as close to the back glass as You can. This will (in this case) leave room for a 90L filter behind it. Take notice of how close the top of the background is to the top of the tank, and if the tilt of the background causes the top to be of uneven height, which will allow undesired water to spill over, into the filter. It may be necessary to put something under the background, to hold it in the right height, which is just below the top of the tank, making sure that no water spills over, at normal water level, but still allows for water to overflow in the event of an accidental blocking of the inlets! After all, it is better to have water spilling into the filter at wrong places, than having it spilled onto the floor...

When the background is satisfactorily placed, it is glued to the bottom and the sides of the tank, creating a reasonably tight seal, so that water may only enter the filter at the inlets. The visible sealing can be camouflaged by pouring dry sand on the glue while it is still wet.


Two RockZolid modules are also installed. One will shield the outlets and the tubes emanating from them, from plain view, and one will make it possible to mount a Tunze 4025 stream pump in front of the background invisibly. Off course they must also add to the aesthetic value of the decor. The first purpose does not leave a lot of choices, as it is given that they must "hang" from the surface, where the installations are placed. Mounting them requires that they are also glued in place, as they would otherwise drop to the bottom or require support from e.g. rocks from below. Fortunately the manufacturer have thought of this possibility, and made a broad flange at all edges, which provide ample room for glue.  They must however, still be kept in place mechanically, while the glue is hardening (app. 24 hours if You want to be absolutely sure). Clamps are the best tool here.

Mounting the two modules. The broad flange mentioned above, is clearly visible on the edges pointing upwards and thus not in contact with any surfaces. These flanges makes it easy to avoid the visible gluing edges seen on the background.
Background filter

The decision to use a full background is heavily influenced by a desire to have a filter with a capacity large enough to decompose waste completely before it clogs, and necessitates cleaning.

There are three practical ways to achieve this; A HMF filter, which is what I use in all tanks currently running, a sump, which I have used before in one of My disbanded marine tanks, and a filter behind a full background.

The HMF filter is, by far, the easiest to mount and also the most affordable, and works splendidly in most cases. It does however, have the drawback, that the sponge used, must be of a uniform and fairly coarse density, to ensure equal flow through all parts of it, and not risk clogging in case of a heavy load. That is why tanks with a lot of lively fish that makes visible dirt drift around in the water, sometimes appear a little cloudy in tank run with this filter type. It is also next to impossible to hide, as it needs to be very large, often covering a whole end wall (it is not as bad as it sounds though, since the uniform dark surface sort of "disappears").

A sump is in principle just a part of the tank that is invisible, allowing installation of any filter (and other technical installations) with comlete disregard to aesthetics. Most filters placed in a sump, looks very much like the ones used in a background filter, so the difference here is mostly that the sump actually adds to the amount of water in the system, and does not take up much space in the tank. The drawback is, that it requires heavy modifications to the tank, mainly by drilling holes in the glass for in- and outlets and installing an overflow box. There is also a price penalty, as the required pump have to have a significant lifting capacity, which invariably results in a high power consumption. Last but not least, the system needs attention, and often have to be adjusted, and water changes is not quite as easy as with other filter systems.

The background filter avoids the drawbacks of the sump, and still allows for a very large filter, that can be totally invisible. It does off course, take up a lot of space, and is not really suited for tanks with more height than width, as it will leave too little space for other decoration, and become foreground as well as background! On the other hand, the right background, whether it be a DIY project or one of the many ready-made ones, can be of significant aesthetic value for the setup, as a basis for a very beautiful interior.


The principle of the background filter is no different than any other biological filter;  Water is forced through a filter substrate, preferably with as large an areal as possible, on which bacteria lives and do their job of decomposing waste from the animals in the tank. This is achieved by pulling water into the filter at one end, and through the filter material and, by pumping it out at the other end.
In order to make sure that the filter does not simply stop all not dissolved material (plant leaves, uneaten food, fish faeces) near the inlets and clogging the filter up, the first part of the filter should contain only very coarse material (here bio-elements), that lets these waste products pass by, and only gradually stop them as the current slows down inside the filter. This is where these very large filters really shine, compared to e.g. canister filters, where the current never slows down enough to make this happen, and instead relies on fine filter material, that collects the dirt, but clogs up and need cleaning at regular intervals. Even the enormous volume of the background filter (in this case 90L coarse filter) is not enough to ensure totally clear water, so the remaining debris is stopped by a finely meshed filter (here densely packed filter vat) This filter could easily clog, but since the large coarse filter has already removed almost all dirt, and the filter is relatively large (8-10L) it will take a long time. People with experience claims that it should be cleaned app. once a year. As this is the only part of the filter that should need maintenance, it should be placed in the easiest reachable end, which dictates where the in- and outlets are positioned. In this case, it was unfortunately the opposite ends of what would have been easiest, regarding drilling and positioning inlets! There`s always something...

It is unfortunately not possible to show the precise layout of the filter, since the tank is placed up aganst a wall, but check the suggestions of the dealer´(the link given in the "mounting the background" section).

It is however, possible to show the layout as seen from above: (the blue text is Danish for direction of flow)
1: Coarse filter. The filter material consists of plastic elements, called "Bio elements", which is shaped to yield large a surface/volume ratio and a lot of possible places for debris to settle in. This part of the filter starts at the opposite end of the tank as shown here, and has a volume of more than 90L.

2: "Box" made from biofoam. Actually a part of the coarse filter, which continues under the box. The purpose is to prevent bio elements to get stuck in the pump`s inlet, and give the pump a resonance free bed. The pump is one of two, each with a capacity of 1500 l/h and placed here because the fine filtervat (4) could have problems if too much water is forced through.

3: Coarse (10 ppm) Biofoam used as separators. They go all the way to the bottom wedged in place between the back glass and the background.  They do nothing but keep the filter materials apart and in place.

4: Filter vat. This vat removes the last floating debris, that has made it through the coarse filter, from the water. In order to let the vat stop all debris, it is advisable not to force too much water through it (see 2).

5: Clear water chamber. The second 1500 l/h pump is placed here. Combined with the first pump (2) it pulls 3000 l/h through the coarse filter, which means that the water on average spends 4 minutes on it`s way from the inlets to here. A water heater could be mounted in this chamber if desired.
The filter pumps

Unimati recommends Aquaclear 70 pumps for this filter, which I can only second, as My experience with the Aquaclear pumps have been only positive. I have had quite a lot of them (most have been sold off, with used setups), and never experienced a breakdown. from a single one. If mounted correctly, they are also very quiet, and can be regulated both in strength and direction! It is however, worth noting that adjusting the flow is done solely by limiting water flow by diminishing the inlet, so the pump is still running at full power consumption, so it would actually be better to get a smaller pump instead.
I use two Aquaclear 802 here, which are identical to Aquaclear 70, just older! (a couple of years ago AC changed the names of their powerheads, but they are still the same construction and strength ). The many possibilities in the pump has necessitated two levers for adjustments:

1: Lever for regulating direction of flow. The shown position is "reverse" as it pulls water in through the exhaust and ejects it through the inlet at the bottom. If the lever is pushed to the left, the red stripe turns green and the pump changes to "normal". This lever MUST be in either full red of full green position! there is no middle way.

2: Flow regulation. This knob simply closes the inlet gradually, and thus regulates the throughput.

These levers are not needed here, as the pumps should run on full strength the normal way. Actually they are only a possible source of failure, since they could be accidentally pushed into a wrong setting, when the pumps are maneuvered into the rather cramped spaces they should go, so it could prove beneficial to dismantle the pump and remove the yellow part:

The other parts MUST be put back again, or the pump will lead a good part of the flow out through the slit that is left open, but they could be glued in position if You want to make sure that nothing can go wrong. Just remember, that the lever should be in GREEN position!
As shown on illustrations above, one of the pumps will be placed in a "box" of biofoam, so that will not give problems with resonance noise, but the other pump will come into close contact with a hard surface (the side glass of the tank), which invariably leads to a rather annoying noise.
It is entirely possible to just push a pad of biofoam in between the pump and the glass, but there is not much room, and it may not be able to stay in place when things are pushed around in the tight space, which can lead to various annoyances, so I have designed My very own "anti noise belt", which is shown below:


The "belt" is cut from a block of biofoam. It is important, to make sure that it is made thick enough to reach out over the dimensions of the parts not covered, so that the pump can be wedged in place without any part touching a hard surface. The foam belt also helps keeping the pump in place, as the friction between the foam wall and the belt keeps it fixated.

Water circulation

The 3000 l/h from the pumps running the filter, is not enough circulation for the Mbuna intended to live in the tank, so a third pump is installed. Since this pump is only providing water movement, a Stream pump can be used, and in this case it will be a Tunze 4025 nanostream, which fits neatly behind the right hand module, where it is completely out of sight, but still have a clear shot diagonally across the lenght of the tank.

Water heater

A water heater is probably not needed here, but if necessary, there is plenty of room for it in the clear water chamber of the filter.
With background, modules and technical installations safely in place, it is time to arrange the flexible part of the decor. Apart from the obvious demand, that the fish must thrive in it, it is a purpose of its own to avoid the trap a lot of owners of a full-background-tank fall into, namely that the background ends up being the primary, if not only, decoration, with the rest of the materials used, just present as secondary props and useful hideouts for the fish. In other words, the decoration must present itself as a unity, with the background as an integral part, but still background. It is also important that the whole thing does not end up looking like a stone fence!

In order to achieve this, I have chosen to use a dark granite , with a fairly rough surface. It has a fair resemblance to the background, which makes for a natural look. In addition to the rocks, I have used a large root, which is app. 1/3 of  the total length of the tank. It is all arranged, to form a curved line through the tank, following the "shelf" built into the background (which is the primary reason why I chose this model). It is a Mbuna tank, so I do not have to consider any special needs regarding free bottom area, which I have taken advantage of, to cover almost all of the available area with rocks of different sizes in multiple layers. This should provide a maximum of territories, with the resulting full-coloured males. It also gives a decoration with a natural fall of the rocks, compared to the stacked heaps often seen in this kind of setup. And now We are ready for all the fishies!