How to Add Rocks to An Aquarium

If you’re a do-it-yourself kind of person, and don’t want to pay the outrageous sums stores charge for aquarium rocks, then you may want to consider going out and finding some rocks on your own. Of course you can’t just add any rock to an aquarium, and you need to take many factors into consideration before adding new rocks to a fish tank.

Choosing Rocks

While you can save money by adding local rocks to your aquarium, if you choose the wrong kind of rock, or don’t properly prepared them, it can be absolutely disastrous. Some rocks can alter the pH, or hardness of the water, and this is especially pronounced if you have naturally acidic water. And other rocks can be infested with bacteria and other nasty organisms that can be deadly to your fish.

Common sense should always apply when adding rocks to your aquarium. Obviously, you should never take rocks from a highly polluted area. While it may be possible to remove all of the toxins, the risk is simply too great to your fish. Also, any rocks that easily crumble will create a mess in your aquarium, and should also be avoided.

It’s important to note that rocks from streams or ponds (or any body of water) will likely carry potentially harmful bacteria and other microscopic life. No rock found in water should ever be directly added to an aquarium. This will almost always end badly.

One of the most important things to watch out for is to ensure that the rocks you add don’t contain any metal. Any rocks should be thoroughly inspected for veins of metal, or rust before they are added to an aquarium. These types of rocks can be extremely deadly to your fish, and should be avoided at all costs.

Safe Types of Rock

There is a wide selection of commonly found rocks that are perfectly safe for the home aquarium. They can be found in most areas, and are easy to identify.

These following rocks are generally safe and neutral;

• Slate
• Granite
• Quartz
• Petrified Wood
• Lava rock

Rocks to Avoid

While many types of rocks are acceptable for the home aquarium, there are several types that you should stay away from (unless you trying to actively alter the water chemistry). The type you want to avoid is carbonate rocks. Many of these rocks are able to increase both the water hardness, and the pH – which is great in African cichlid tanks, and not so great in discus tanks.

The most commonly found carbonate rock is limestone. It will have limited effects on tanks that already have basic, hard water, but can significantly impact soft, acidic water. With that being said, there is a limit to how much it can affect the water chemistry. Simply adding some limestone to acidic water will not make it acceptable for African cichlids.

An easy way to test if you have a carbonate rock is to apply a few drops of white water vinegar to the surface. If the rock fizzes, then it has carbonate content and will likely affect the pH and hardness of the water (this may not always be 100% effective and hydrochloric acid is more accurate).

The following are the most commonly found carbonate rocks;

• Marble
• Alabaster
• Dolomite
• Limestone
• Some sandstone
• Some types of sand

Other material that will affect the pH and hardness;

• Coral
• Crushed Seashells

Preparing the Rocks for Use in an Aquarium

Now that you’re chosen some safe rocks that are appropriate for your water type, you need to prepare them for your aquarium. The very first thing that you do is clean the rocks. They should be rinsed off and then scrubbed with a stiff brush in clean water. It’s very important that no household cleaners be used, since most cleaners will leave a residue that could foul your fish tank.

Once all of the dirt and grime has been scrubbed off of the rocks, you can then choose from two methods to disinfect them. The most commonly used method is to boil the rocks, but they can also be soaked in a bleach solution.

Boiling Rocks

I will warn you upfront that there are some dangers to boiling rocks. If they are left unattended, or allowed to boil for too long, the rocks can explode. While this has never happened to me, there are numerous horror stories involving injuries and damaged kitchens.

The safest way to boil rocks is to place them in a large pot where they can be fully submerged. The water should be brought to a boil, and left on the lowest temperature that will maintain a steady boil. The pot should also be covered, and I recommend wearing full safety gear while dealing with the rocks. In the off chance a rock explodes, you will want to have your hands, face and body protected

After the rock has been boiled for about 20-30 minutes, it can be removed from the pot. It should then be placed on paper towels to absorb any excess water, and allowed to cool for at least an hour. The boiling will have removed all of the bacteria and other life forms from the rock. Once it has been allowed to completely cool, it can be safely added to your aquarium.

It’s also very important to note that this method won’t work for porous rocks. If you attempt this with lava rock or other similar rocks, they will most likely break apart or crumble while being boiled.

Using a Bleach Solution

The second method is less effective than boiling, but is the best option for porous rocks. This method can also be used if the stones are too large for a conventional pot, or you don’t want to deal with the dangers of boiling rocks..

All that needs to be done with this method is to find a container where the rock can be fully submerged. The container should be filled with a 10 to 1 water to bleach solution, though some people use a slightly higher concentration.

Once it has been submerged in the bleach solution, it should be allowed to sit for 24 hours. At the end of this time, the rock should be removed, and washed thoroughly with clean water. The rocks should be rinsed under tap water, and then dipped in a bucket of treated water to remove any trace of the bleach solution.

How to Safely Add Rocks to an Aquarium

Now that you’ve properly cleaned your rocks, you can just throw them in your aquarium – right? Well, not exactly. While you likely won’t run into any problems if you’re just placing a few rocks on the substrate in your aquarium, there are still a few things you need to watch out for.

One of the biggest mistakes that people make when adding rocks to their fish tank is to pile them up against the glass. Rocks are heavy, and aquarium glass isn’t particularly strong. If you pile a sufficiently large pile of rocks against your aquarium’s glass, it will crack. They should always be piled away from the glass, in safe piles.

Which brings us to our second point – always secure rocks in an aquarium. It’s rarely safe to pile rocks together in an aquarium without anything to secure them. All it takes is one overly excited fish, or a simple bump to the aquarium to send the rocks tumbling. And once the rocks fall, you’re either going to end up with some crushed fish, or broken glass. Either way, it won’t be pretty.

Because of this, I always recommend using aquarium silicone to glue the rocks together. Even if you’re just created a small cave for your fish to hide in, it’s still a good idea to safely secure it with silicone. Always make sure to use a non-toxic silicone, and I recommend using Aqueon Aquarium Silicone.

If you follow these simple steps in choosing your rocks, and safely secure them, you will have created an attractive and affordable habitat for your fish.