Filter behind Slimline

If you prefer to hide filter, heater or pipes behind a Slimline - this article is for you. We will conceal a filter behind a Slimline Basalt/Gneiss, though this method applies to all Slimline models. All you need is aquarium silicone, a felt pen, and something to cut – or to saw with. The material of the Slimline series is very strong – but easy to cut or saw through, making it very adaptable to your needs.

Products used in this article;

Space for the filter

We are using two Slimline sections in a rather small aquarium. The first section will be glued to the back glass, but the second will be installed about 5 cm in front, and overlap the other. The first step is to decide on which section you want to place at the back of the aquarium.

This is the filter that we are planning to make, seen from behind. The first section will be glued to the back of the aquarium, the other will conceal the filter and the heater. The filter itself consists of a piece of filter sponge and a circulation pump connected to a hose. The water will flow in through the sponge and is pumped out through the hose.

Estimate where the sections will overlap each other. Turn the sections around and mark with the felt pen on the backside where you want to trim off. The easiest way is to use the aquarium as guide.

Cut to size and glue the first section

Cut Both sections to size with a thin bladed knife. Cut many times in the same track, or if you use a saw - make sure the saw is as horizontal as possible when cutting to avoid chips to loosen from the front.

Check the pre-cut sections once more before gluing the first section to the back glass. Turn the first section around and apply aquarium silicone on the back, then press it firmly against the glass. Do not mount the second section, which will cover the filter yet; we’ll construct the filter first.

Making the filter

Now that the first sections is glued in place, we want to estimate how large our filter is going to be. Measure the width of the circulation pump and cut a piece of filter sponge, a bit thicker than the the pump size, using your best bread knife. The sponge should be as high as the tank and the width should leave sufficient room for the pump and heater. Cut a hole for the hose in the filter media and connect the pump to the hose.

Put the sponge, the pump and the heater in place. The sponge will work as a guide when we glue the last Slimline section in place.

Mounting the last section

Wedge the section into position using a piece of wood or something else that will hold the section in place while the silicone cures. The Slimline section should press the sponge firmly, so that the sponge is held in place by the section.

Try to put the section in place with the wooden piece a few times, without having any silicone on it, so you learn how to do it without shaking and smearing silicone all over the tank. Then apply silicone to the side and bottom edges, and practice what you’ve just learned. Do not apply any silicone on the back of this last section, only on the edges – you may want to take the sponge out for cleaning sometimes.


Now you are finished. The Slimline sections are mounted and the filter will be very easy to remove for cleaning in the future. Wait for 12 − 24 hours until the silicon has dried. Then you can fill the aquarium with water. Enjoy your Slimline background with the concealed filter!