By Jacques Bouchard
For a beginning aquarist, choosing the right gravel (substrate) for your tank can seem as simple as choosing your favorite color and running with it. And while the “curb appeal” of an aquarium — its gravel and decorations — are definitely a major part of the hobby’s appeal, there’s a lot your gravel can do for your aquarium’s beauty, as well as the health and behavior of your fish.
What you choose for your substrate is, both literally and figuratively, the foundation of your aquarium, and a little planning can go a long way to a beautiful, successful system. Before committing to an aquarium substrate, take a moment to ask yourself these four questions:
1. Why Use Aquarium Gravel At All?
In some cases, the wise choice could be to not have any aquarium substrate at all. This is most common when an aquarist has many tanks and keeps a small one empty as a “hospital” tank for sick fish. It’s also common when a fish owner is keeping large fish in a tank that may be too small for them. In these cases, a no-gravel approach aids in waste removal, allowing the owner to keep things extremely clean when doing water changes.
Generally speaking, however, adding gravel to your aquarium is a wise choice. In particular, gravel becomes the home of beneficial bacteria that will break down ammonia from fish urine and waste into nitrites, and then transform nitrites into nitrates, which are less toxic for the fish. They also become anchors for the roots of live plants, which can do wonders to add beauty, balance your water chemistry, and add oxygen to the water.
Depending on what you use, your aquarium substrate can have an impact on the overall water chemistry of the tank. For example, adding crushed coral or aragonite will harden water, add a PH buffer, and often add minerals to the water that are beneficial to some types of fish.
With that in mind, if you’re selecting a colored gravel, you’ll want to make sure that it’s been created with a “polymer seal”. The dyes in the aquarium are not always healthy for the fish if they bleed into the water, and these seals can help to protect them. They can be very intense too – I’ve ruined strainers permanently with the dyes off bags of black gravel.
2. What Will Be Living In Your Aquarium?
Choosing the right gravel or substrate for your aquarium should be based on what’s living there, including:
If your fish will be living in it: Many species of fish, such as stingrays (There is a freshwater variant!) or Kuhli loaches will try to hide in your substrate, and they’ll need fine-grained materials to survive there without being harmed. Scavenging fish such as goldfish can also have larger pieces of gravel become lodged in their mouths as they forage for food. All fish will come in contact with gravel from time to time, so the best gravel should be round-edged to avoid scratching. If your aquarium inhabitants are big waste producers like large catfish or turtles, large-grain gravel or even glass marbles are the easiest to vacuum, and could be the best choice for you.
If you have live plants: Plants have roots and delicate stems, and unless you’re using dirt as your substrate (which is best left to the experts), they’ll be hungry for nutrients. Large gravel can damage stems as you plant them, and the roots hold better to smaller-grade gravel. Sand offers a lot of hold for roots, but deeper areas of sand can develop anaerobic bacteria (bacteria that grows without oxygen), which is thought to deter root growth.
Generally, fine gravel is a cost-effective choice that works well with plants. A better but much more expensive choice is to purchase “activated gravel” — a porous, nutrient-rich gravel that provides out-of-the-bag readiness for planted tanks. Along with this, some dedicated aquarists will create layers in their tank that promote healthy plant growth, such as adding a layer of peat moss to provide needed minerals for plant growth.
If you keep snails: Common aquarium snails (sometimes referred to as “pest snails”) can be a benefit to your aquarium’s gravel bed. Two of the three common types of snails found in aquariums — Physa and Trumpet snails – are known to burrow into the gravel, with trumpet snails being particularly enthusiastic burrowers.
Unfortunately, Trumpet snails are also extremely prolific and nearly impossible to eliminate from an aquarium once a population is established. Additionally, they can begin to look bedraggled as they reach a point where there’s hundreds roaming your aquarium, and they’ve bred beyond their food supply. The other burrower, Physa snails, are easier to control but don’t churn up the substrate as well. Ramshorn snails are easier to control and even come in brown, gold, blue, and pink varieties, but will only clean the surface of the gravel.
If you want to deter snails from growing in your aquarium, large-grain gravel is hardest for the burrowers to hide in, and the best way to go.
3. What Will It Look Like?
Bubbling treasure chest ornaments and neon-pink gravel adds a fun look to your aquarium, but it also moves the focus away from the fish and on to the decorations. If you prefer this approach, there’s many ways to create that environment in a healthy aquarium. Be sure to do your research on each item you choose — many of the very common aquarium substrates and decorations (like plastic plants) can be very harmful to your fish. It’s also a good idea to plan for your gravel vacuuming as you place your ornaments, as you will want to be able to access your gravel without damaging your setup.
It’s very popular, particularly in Europe, to create a “planted” aquarium — an aquatic garden with minimal fish. If your focus is on the plants, many aquascapers prefer brightly-colored gravel as the best complement to the natural green foliage. In the long run, however, planted aquariums usually include a “ground cover” plant, such as baby tears or grasses, which cover the visible part of the substrate in plants. In this case, your top priority would be to create a layer of substrate that will help these plants grow.
If you’d like to highlight the beauty of brightly-colored fish, a darker-toned gravel is usually the best choice, as it can best highlight their natural colors. Additionally, darker colors tend to have a calming effect on fish, and the lower stress levels help to bring our their most vibrant colors.
Personally, I buy fish for their behavior and personality, and rarely own brightly-colored fish. My approach has always been to pick a neutral-toned substrate and build the aquarium to look like as natural a setting as possible, highlighting plants, layout, and the fish themselves equally. The picture below is of my 72-gallon bowfront setup.
4. Where Are You Putting Your Gravel (And How Much Is There)?
How thick your aquarium gravel layer should be has been hotly debated in forums and communities over recent years.
The “old” way of thinking is to use a deep layer of gravel to house bacteria and create space for deep plant roots. Recently, however, this practice has been contested by aquarists who point out that deep gravel and sand beds trap debris and may promote anaerobic bacteria growth that can lead to harmful hydrogen sulfide gas pockets, as well as deter root growth (anaerobic bacteria is also an important piece to the cycle of breaking down ammonia). It’s also true that using a gravel vacuum on deep layers of gravel will send old waste and debris into the aquarium, causing harmful spikes in levels of ammonia, nitrites, and nitrates.
In my experience, plants have thrived in gravel layers of many different thicknesses – or even in no substrate at all. I’ve seen aquarium roots plow through more than ten inches of gravel and bunch up at the bottom of an aquarium, and have had small aquarium fish live for seven years or more in the same aquariums. The trick seems to be to vacuum only the surface layer of the gravel, rarely going for a “deep dive” of more than three inches into the substrate.
I use a layer of gravel about five inches deep, but never clean all the way to the ground when vacuuming. On the rare occasion when I change the gravel, I remove the fish entirely and house them in a different aquarium overnight afterwards, doing a heavy water change and adding new filter media before moving the fish back in.
Whatever you choose, be creative with your gravel setup! Have fun with the process! Who says it has to be a single layer along the bottom of your aquarium? Develop a unique look to your aquarium by varying the depth of your gravel in various areas and creating unique areas and setups.
For example, I love to create catfish caves with gravel on top, and plant roots growing through the gravel into the cave. I do this by building a cave with a rock wall along the edges, using aquarium silicone to seal the rocks together (see photo below). I add a layer of large-grain gravel, which clogs up any small holes, then fill the rest of of the space with fine-grain gravel. The effect is quite unique!
Guest Author Bio:
This guest post was contributed by Jacques Bouchard, an aquarist of 20 years and Senior Digital Marketing Strategist at DragonSearch. Follow him on Twitter at @DSFido to find more of his articles on aquariums, or to ask any questions you may have about your own tank setup.
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