How to make a rocky tank background


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Jeremy Gay uses lava rocks to turn his aquarium into an underwater grotto in this step-by-step guide.

This is an easy weekend project. The effects are long lasting and your fish will appreciate it. I've utilised lava rock, a widely available and pliable rock that's light in weight, easy to break with a hammer and can even be cut with an ordinary saw.

By smashing it up and gluing to the back of the tank I’ve created an aquarium background — and by following these steps you can create one too.

A rocky background can help turn your plain tank into an underwater world and with lava jutting out here and there you can also create a grotto effect. Why stop at the back of the tank? Clad the sides in rock too and you have yourself a great cave effect.

Fish feel more secure with a three-dimensional background and, with the porous nature of lava, it will all become live with beneficial bacteria, aiding filtration.

If you're a keen plant grower you can imagine some Java fern, Anubias and mosses growing off it, gelling together to become one living background. Using small chunks of lava you can clad virtually anything — like Juwel filters and corner weirs. It’s great for hiding other equipment too. Give it a go!

What you’ll need

  • Lump hammer
  • Two large tubes of aquarium silicone
  • Unipac lava rocks, 10kg
  • Tank
  • Protective eyewear

Time taken

Two hours for this 60cm/24" tank, plus 24 hours to allow the silicone to cure.

Cost at a glance

Two large tubes of silicone £20

10kg Unipac lava £22


When smashing the rocks, goggles are vital. As well as the inertia of big chunks, smaller nuggets can take off like bullets. Take care!

How to make your background

1. To hide pipework and equipment I’ve used June issue’s drilled aquarium, complete with bulkhead and rigid pipe. I’ve slipped another pipe over the top to ensure I don’t stick anything directly onto the pipe. This way I can still access and remove the pipe for maintenance.

2. Take a lump of rock and smash it up with a lump hammer. Wear protective eyewear for this job as bits may fly off. I’ve aimed to break up the rocks into chunks two or three inches in diameter. Then I’ll use the smaller pieces and dust later on.

3. Lay the tank on its back and start to glue the chunks into the rear corner using silicone. Either place a blob onto the back and press the rock into it, or place silicone directly onto the underside of the rock and press it into place. Either way will work.

4. Continue across the back working left to right, pushing the rocks together and selecting so they produce minimum gaps. Give them all a little shake to make sure they are all in contact with the silicone underneath. Once covered leave for 24 hours.

5. Twenty four hours later I hesitantly tip the tank to the right way. A few crumbs fall off, but all the bigger rocks have stuck and fused together to make my 3-D background. You’ll see the left-hand ones sticking further forward as these mask the pipe behind them.

6. To make the aquascape even more three dimensional I’ve made a small pile of larger rocks in the midground. Use as many as you want to create an even more rocky aquascape and, if you want more perma-décor, stick the larger stuff together to make tall structures.

7. I’ve found lava-like aquarium substrate in the form of this Caribsea Flora Max Volcano Red. Again it is highly porous, so creating loads of homes for bacteria. It’s also said to be good for plant growth. Just don’t use it with any digging fish as it has rough edges.

8. The finished furnished tank. No equipment is on show and exactly the same principles could be used to hide heaters and internal or external filters. If you want something different in the future, razor blade off those silicone blobs and the whole thing will peel off.

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