Stacking Rocks in Your Aquarium

Published March 23, 2009 - RSS/XML Feed

By Robert Lashlee

One of the ways you can add personality and a natural look to your aquarium is by the addition of rocks. However, when you use rocks in your aquarium to forms caves or piles, you are mixing two things that traditionally do not mesh well: rocks and glass. Therefore, it is very important that you follow several rules when adding rocks to your aquarium so that you do not come home one day to shattered glass and water covering your floor.

Why Would I Want Rocks in My Tank?

This is a valid question to start with. Rocks add a great deal of interest to your tank because they block the view of the entire area. For example, when your tank is bare, you can see all your fish all the time. This can become quite boring. On the other hand, when you break up the space with caves, you may see a fish come out from underneath a rock, then head towards the back while another one circles around the pile of rocks on the left. I think you can imagine what I am talking about. Rocks give the fish their canvas on which to paint. It adds personality by giving them something to interact with and at the same time keeps the look of your aquarium fresh because you will not often see the same exact fish out in the open together.

Rocks are also useful for some natural reasons. For example, many African cichlids eat algae off rocks so supplying them with a nice bunch of rocks better simulates their natural environment and behaviors. Rocks can also serve to break up aggression by giving each fish their own territory to defend (so they are not defending the entire tank).

Okay, I’ll Put Some Rocks In, But How Do I Stack Them?

This is generally the first question someone asks after they have decided to put rocks in their tank. The answer actually lies in what kind of rocks the person wants. Are they smooth or jagged, large or small, etc.

If your rocks are smooth then you will have one of two options. Your first option is to make your stack very short, almost forming a small rubble pile. An example of this is pictured below.

Your second option is to use silicone to glue the pieces together. Be aware though that once you glue them together, they are stuck that way. Some species (such as mbuna cichlids) require you to change the rock work around from time to time in order to break up territories. This is not possible when you glue the rocks together. You might also get bored of the same look day after day. One of the great things about rocks is the ability to make your tank look completely different with each restructuring of your rocks. This is not possible when you glue them together.

Now, if you have jagged rocks, such as lace rock, then your stacking becomes much easier. Simply start by making a nice wide base that is firmly in the substrate. Then add rocks in layers making sure that each rock is very stable (remember, fish can bump into them and knock them over). I usually try a rock at a certain location and then push on it in all directions. If it shifts then I move it somewhere else. It takes some time, but it is well worth it in the end as the result is a very stable wall. The jagged edges allow you to fit everything together like a puzzle.

As you build your way up, you want to taper the rocks so that the stack is narrower at the top and does not lean against the back glass. Here is a cartoon example of what your general rock wall should look like.

You also want to make sure you match the size of the caves formed in the rocks to the size of your fish. You generally want them to be able to swim in between the rocks to give that natural feel, but if the spaces are too large or too small, the fish will avoid them.

How Do I Make Sure They Don’t Break the Glass?

There are three main ways to make sure your rocks do not break your glass.

Don’t add too much weight – Remember that you cannot just keep stacking and expect your aquarium to hold it. There are limits to everything. I tend to use about double the weight of rock as gallons of water in my tank (so for example, in a 55 gallon tank I use 110 lbs of rock). This is just a general rule for me because it usually provides me with more than enough rock to make large stacks and I have never had a problem with this much weight on my glass.
Don’t make pressure points – You don’t want a tip of rock resting on your glass, especially if that rock has rocks on top of it applying even more pressure. Every time you have points against the glass, there is a chance that the glass will break from the pressure. In general, you don’t want your rock leaning against your glass walls. Instead, stack the way I showed you above. This is the safest method. You also need to make sure there is a layer of substrate between the bottom glass and your rock. Sometimes, you can push on the bottom layer so much that you end up moving all of the substrate out of the way and the rock has points that then hit the bottom glass. This is obviously bad. If you are going to have a good deal of rocks in your aquarium then you will need a thicker layer of substrate to disperse the weight.
Make sure your rocks are stable – Remember that fish can dig out substrate and bump into rocks all the time. Therefore, you need to ensure that they are not going to dig out the area under your rocks and that the caves are so secure that they will not fall when bumped in to.

If you are really worried about the weight of the rocks then you can always buy egg crate at your local hardware store and place this under your substrate. It helps to disperse the weight, but can be a pain when it comes to deep vacuuming.

What Kind of Maintenance is Required?

Rocks do add to your cleanup time, especially if you have a lot of them. They make it almost impossible to catch fish which usually means you need to take a bunch of them out to catch one. Food and waste also gets caught underneath them which means every month or two, you need to take all of the rocks out and vacuum the substrate where they were. However, things like these are well worth it for the look of a nice rock tank. See what I mean below.

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