What type of substrate should I use in my aquarium?

One of the major components to an aquarium is going to be the substrate. There are all different colors of gravel, different sizes of gravel, different colors of sand, different sizes of sand, or having none at all. What is the right way to do it? Or, is there a “right” way to do it? When considering what type of substrate to use we must first ask ourselves what we are trying to accomplish. What type of animals are we housing? Is this our first time setting up a tank? The fact of the matter is that there is no correct way to implement (or not implement) substrate, but there can be pros and cons to consider depending on what direction you would like to take the aquarium in. 

Although aesthetics are a component, there can also be major benefits to having substrate or no substrate. First and foremost, whether it be sand, gravel, or larger stones, these all have surface area. But what does that mean? Well, surface area on substrate (some more porous than others) is essentially real estate for beneficial bacteria to grow on. This will help with the breakdown of ammonia which can be very harmful to our aquatic animals. Having said that, this will help us get through the initial cycle of the aquarium and help with what a lot of people refer to as “the ugly stage” of a tank. But on the other hand, if not cleaned on a regular basis this can lead to pockets of detritus (food and waste rotting away). And, if left unattended, this can and will lead to a spike in nitrates that can be very stressful and even fatal for fish and invertebrates. The bottom line is that if we have substrate (gravel, sand, or stones) we must clean it as a regular part of our maintenance schedule.

If we decide to go with a bare bottom tank we will be looking at the pros and cons of this matter in an opposite way as we do with substrate. We will have no sand or gravel to clean so we will not need to do that and we will not have to worry about the so-called “pockets” discussed in the previous paragraph. We will need a way though to flush what could become a dead spot as far as flow is concerned. We can do this by either positioning filters near these areas, by aiming returns to compensate for these areas, and/or (a more common solution) implement power heads and wave makers. As far as surface area for nitrifying bacteria to grow and establish, well, we do not have that any more as far as substrate is concerned. We will be relying on decorations/rockwork, filters, sponges, bio-media, and so on. Pertaining to the first six to twelve months of an aquarium, this can be challenging. There tends to be more algae blooms, bacterial blooms and makes for a longer “ugly stage” in the beginning of a tank’s life.

What type of substrate should I use in my freshwater aquarium?

Again when asking this question there is no “correct” answer. But for our sake we will dig into what is more common to use. We will need to discuss what we are going for in this freshwater aquarium. Is this going to be a cichlid tank? Is this going to be a tropical community aquarium? Are we going to have plants and will we need to rely on nutrition through our substrate? These three goals are some of the more common goals when an aquarist is setting up a freshwater tank. And again, we will discuss some more “common answers”. This is not to say that there are either variations out there or we would not be able to get away with and have success with other substrates in any given application. 

When going after a cichlid tank, we will want to consider sand and/or river stones. Most cichlids are “rock dwelling” - this should be taken into consideration when shopping for substrate for a cichlid tank. Cichlids will typically like to move the sand around in their aquarium, re-decorate if you will. It may be wise to note here this will be one of the simple facts as to why plants and cichlids will not be great tankmates. Again this is not 100% of the time, just mostly. Another great thing about having a mixture of river rock and sand in the tank is the sheer surface area we will have to grow nitrifying bacteria to help with breaking down ammonia. Gravel can also be used in a cichlid tank. The decision between gravel and sand will be aesthetics. 

For a tropical community fish tank hands down the more common selection is going to be gravel. This will provide the surface area for beneficial bacteria and will be easy to clean. Gravel will come in all shapes, sizes and colors so whether we are setting up a nice tank for our office or a Finding Nemo themed aquarium for our kids, there will be a color and size of gravel that fits your needs. 

Planted tanks are a bit of a different animal. This will really depend on how “high tech” we are going with the planted tank. I have seen gravel, sand and DIY soil/substrates for planted aquariums. A nice and safe middle ground though would be any commercially available premium natural substrate geared towards sustaining plant life. If we have sand or gravel as substrate and we now want to incorporate plants into our aquarium it may be unnecessary to completely change all of the substrate. There are plant food and/or root tablets that can be purchased at your local fish shop. These tables will need to be pushed into the substrate to promote nutrients within the gravel or sand. But again this may not be enough if we are going for higher maintenance plants. The implementation of these root tablets could be all we need if we are going for lower demand plants. It would be hard to take a community tank and convert it into a “high tech” planted tank. This would require much more than gravel removal. Honestly, the substrate would be the least of our worries. But if we were going to jump from a non-planted tank to a “high tech” planted tank we would want to consider the appropriate substrate. 

What type of substrate should I use in my saltwater aquarium?

When setting up a saltwater aquarium we will need to ask ourselves really only one question - Will we have coral or will this be a fish only aquarium? The reason we should know this is to determine what type of flow, lighting and substrate we will put in/on our tank. Again, no matter what we decide to do with our tank, there is no one size fits all answer. I have seen show-stopping reef tanks with large sand, small sand and no sand. Is one right and one wrong? The answer is no, neither is wrong nor right. It is simply a different approach to a reef tank. But as mentioned above, there will be pros and cons that correlate with having or not having sand in the saltwater aquarium. 

Let's take first the tank that will be fish only with live rock (FOWLR). This would be one of the better candidates for very fine sand. Reason being is that we can always aim our power heads and return away from the sand to avoid creating what may look like sand dunes. But here again, we may be creating “dead spots” which will inherently collect detritus. This would be one of the reasons many would consider staying away from finer sand and purchasing crushed coral or larger sand. Even with minimal flow fine sand will be easily pushed around. But many find the fine sand appealing and would like to see it aesthetically. If we want to go with no substrate in a fish only tank we will want to make sure that we have ample biological in our sump. Fish only systems tend to be “heavy” in the bioload aspect and we will want to ensure we have plenty of nitrifying bacteria to support the load. Generally speaking for this reason coupled with sand aesthetically looking nice is why we will typically see some kind of substrate in a fish only saltwater aquarium. 

Lastly let’s talk about a reef tank and the pros and cons of having or not having substrate. There are many different types of reef tanks out there; mixed reef, SPS dominate reef, frag tank, softy tank and so on. I would say that all forms of these different reefs can definitely benefit from having substrate as long as cleaning the sand is within the maintenance schedule. The sand will allow for beneficial bacteria to establish and grow. In the “pros” aspect of this it will also look very nice as well. Most of the cons have been discussed in earlier paragraphs. A coral tank will require flow (a lot of it too - depending on the type of coral in it) and this may create sand dunes and in worse case can blow sand onto delicate coral. Also, if not maintained, it can lead to those detritus pockets previously discussed. Now for the bare bottom tank while housing coral. I will say that SPS tanks and frag tanks are more common to have bare bottoms. SPS will sometimes have a bare bottom to accommodate the high flow that these corals require. This will allow for power heads to be placed low in the tank to “flush” detritus down the drain into the sump. Frag tanks are along the same lines, They will have no substrate for ease of cleaning. This all sounds nice in the speaking but if we do not have bio and surface area in our sump it will be very difficult for bacteria to establish. This can lead to algae and bacterial blooms and a longer “ugly stage” of the aquarium. It has been said that if you can be patient for a year or two for a bare bottom reef to establish, it’s well worth it. We must remember though that in these bare bottom systems it is crucial to have the surface area somewhere else for the bacteria to grow. 

In closing, substrate plays a large role in freshwater or marine aquariums. It is a multi-purpose aspect of our hobby. Sure it looks good but a lot more is going on that the human eye can not see. When deciding if substrate and what type of substrate is right for you, ask yourself what you would like to accomplish with the tank. And from there we can outweigh the pros and cons to make an educated decision.

January 7, 2022
Nick Coleman