Adding Rocks and Wood to Your Freshwater Aquarium
Published March 11, 2008
Written by Katherine Barrington
Learn about the things you should consider when adding rocks and wood to your aquarium.
Many individuals love the look of rocks and/or wood in their aquariums. Rocks and wood help to provide a natural look and often gives fish a habitat similar to their native one. However, there are several important things to consider before adding either of these objects to your aquarium. This article will discuss these considerations along with the pros and cons of using rock work and wood in your freshwater aquarium.
There are several advantages associated with using rocks or wood in your aquarium.
● If your fish require a certain set of water parameters, rocks or wood can be useful in attaining these naturally (in other words, without chemicals). For example, many types of rocks, such as Texas Holey Rock and Limestone, serve as a buffer and will raise the pH of your aquarium. Driftwood, on the other hand, will often lower the pH and soften the water.
● Some fish species eat algae off rocks or wood in their natural environment (some fish eat the wood itself). Providing these fish with rocks or wood in an aquarium setting allows them to do something instinctual while providing them with a healthy, natural diet.
● Rocks and wood provide a great deal of surface area for the nitrifying bacteria to colonize on. These bacteria help to eradicate ammonia and nitrites from your aquarium – important since both of these substances are toxic to fish.
● Many aquarists prefer to keep fish in a habitat similar to their natural one. This is not as important as in years past because many species are now bred in captivity, but it still can be quite a scene to watch fish thrive in an aquarium modeled after their native environment.
● Rocks or wood can provide hiding places to fish that need this kind of environment to escape other aggressive species. It can also make fish feel safer if they are used to living in caves created by the rock or wood. Additionally, some species breed or lay eggs on these objects.
● The final advantage is purely aesthetic. Elaborate rock work or a beautiful piece of driftwood can often make your tank look spectacular. For hobbyists who prefer the natural look, it is hard to go wrong with adding stones or wood to an aquarium.
There are also several disadvantages with using rocks or wood in your aquarium.
● If you keep a great deal of rocks or wood in your aquarium, it can be difficult to properly clean the tank without removing them all. Uneaten food and debris will often get trapped back in the rock work and will end up working its way down into the substrate beneath the rocks. Vacuuming this covered substrate is impossible unless the rocks are removed. If you decide to have a stack of rocks in your aquarium, be prepared to remove them at least once every one to two months to vacuum up this trapped debris.
● Rocks and wood also make it difficult to catch fish or remove dead ones. With so many places to hide, often a significant amount of the rock or wood needs to be removed in order to catch any fish (assuming they are not slow moving).
● Certain rocks or wood can be harmful if your fish prefer a certain set of water parameters that are the exact opposite of what the rock work or wood create. For instance, if you put driftwood in an African cichlid tank, the cichlids prefer a high pH while the driftwood is creating a more acidic environment.
● Most rocks weigh a great deal. The glass or acrylic used with aquariums is very strong, but not without limits. Do not stack too much weight against the back glass of the tank or stack too much weight on the bottom. A good precaution if you are going to stack a lot of weight up is to buy some egg crate at a hardware store, cut it to size, and put it on the bottom of your aquarium (underneath the substrate). This will serve to better disperse the weight of the rock work.
● Sometimes, rocks or wood can create a poor visual look. For instance, driftwood can stain your water with tannins if not boiled properly before its introduction. This may be the look you are going for if you want a “black water” aquarium, but you may also hate it. Also, rocks and wood provide additional surfaces for algae to grow on. A subtle layer of algae looks very nice on these objects, but if large clumps start to form, you may not like the look.
How to Tell if a Rock or Piece of Wood can be Used in an Aquarium
A common question is, “I found this rock (or piece of wood) outside – can I use it in my aquarium?” The answer is that there are several points to consider and test before placing these objects in your tank.
The first general guideline for wood is to boil it for several hours or soak it for a period of time. Boiling tends to kill any bacteria present in the wood and makes the wood water-logged so it will sink. If the piece of wood is too large, many people use a cheap trash can or tub to soak the wood in hot water. Keep adding hot water and scrubbing the wood for several days to a week. Soaking the wood also helps to remove tannins, but this can sometimes take up to a month to remove them thoroughly. Tannins will stain your water, but the amount of tannins leached into your aquarium will depend upon your specific piece and type of wood. You will need to replace the water in the tub every so often and it usually takes about a month for the tannins to reduce to the point where they will not impact your water color. Also, do not bleach the wood as it will be hard to remove from all the crevices and boiling does just as good of a job.
Boiling rock work does not harm the rock in most cases and is done by some aquarists, but it is not really needed. Instead, give the rock a good scrubbing and soak it in hot water to clean it up. Never bleach your rock; it is hard to get rid of the bleach and it is most often unnecessary.
Once your rock or piece of wood is clean, make sure it will not crumble in your aquarium. To test this, wash the object in some water, and brush it with a hard brush. Then let it soak in a bucket of water for 24 hours. Brush is again. If a significant amount of the rock or wood is still flaking off, it is probably going to degrade in your aquarium.
The vast majority of fish prefer a neutral environment. Therefore, rocks that raise the pH or increase the hardness of your water should be avoided in most cases. Below is a partial list of rocks that are suitable for aquarium use, but that will raise the pH and/or hardness of your water:
● Texas Holey Rock
● Petrified coral
The impact these substance have upon your water is often overstated. If your water is already approximately neutral (in the 7s), these rocks are probably only going to raise the pH by several tenths. This is hardly enough to impact most fish. However, if you have slightly acidic water (less than 7) and intend to keep it that way then these rocks can have a large impact on the pH. The effect also depends on the buffering capacity of your water (relates to the hardness or softness of your water).
If you are unsure if a certain rock or piece of wood will impact your pH and/or hardness there are several methods you can use to test. First, you can add some drops of vinegar on the piece. If it fizzes then it will raise the pH. This method is not always accurate, however, and a more complete test is to drop dilute HCL (can find at hardware stores) and see if it fizzes. As an alternative, you can place the rock in a bucket of water for several days and see how it impacts the water by running pH and/or hardness tests.
You should also avoid rocks that will introduce heavy metals into your tank. Common culprits are rocks with rust spots on them and pyrite (fool’s gold). If you see metallic looking veins running through the rock, it is generally not a good idea to introduce it to your aquarium. Pyrite should never be put in an aquarium.
Finally, be cognizant of where you found the rock or wood. Did you find it in a heavily polluted area? If so then it may contain contaminates that can kill your fish. Was the rock or wood submerged in water? If so then there may be harmful bacteria or fungus growing on it. Just be aware of the environment the object came from and use common sense.
Recommended Rocks and Wood to Use in Your Aquarium
Below is a list of rocks and woods that are generally recommended for aquarium use. However, remember to think about the considerations discussed above as well as the environment you are creating in your aquarium. Not all of these rocks will work with every species of fish.
● Lace Rock
● Texas Holey Rock
● Pumice or Lava Rock (assuming the piece of pumice will sink)
● Petrified wood
● Mopani wood
● Driftwood – if you purchase driftwood from a store, make sure it is aquarium safe and not only for reptile use – also, never use driftwood from the ocean in a freshwater setup
Adding rock work or wood can really enhance the beauty of your aquarium. However, you need to ensure that the objects you put in your aquarium will not adversely impact the environment. This article is meant to make you aware of the considerations you need to make in determining if a rock or piece of wood is indeed suitable for your tank.
For additional information, refer to the following web pages:
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