If you’re an experienced aquarium keeper, you already know that one of the best things about the hobby is the endless variety of options that it offers. You can choose from saltwater or freshwater tanks, live plants of plastic castles, and anything from a small bowl to a hugely complex operation. A quick trip through your local supply store will give you an idea of just how much there is to choose from.
What works better in a fish tank, marbles or gravel? Both marbles and gravel are popular substrates for aquariums. Depending on the size of your tank, the type of fish that you are keeping, and your personal preferences—one will probably be better than the other. It all comes down to what you are trying to achieve with your aquarium and what you are or are not willing to do to get it.
You’ve probably seen large aquariums with multi-layered substrates that are full of lush living plants. You’ve probably also seen fish bowls with a layer of beautifully colored marbles serve as a home for a single betta fish. If you enjoy fish, you can choose to set up a bowl or tank that falls anywhere along the spectrum between the two. It’s just a matter of knowing how to create a set up that works for you.
What Will Work Best in Your Fish Tank?
There are a few different things that you need to consider when you’re trying to figure out what will work best for you in your fish tank:
- Fish Tank Size: One of the most important things to think about when you’re choosing a substrate material is the size of the tank that you’re going to set up. The pros and cons that are unique to gravel on the one hand and marbles on the other mean that each is particularly well suited to tanks of particular sizes.
- Fish: Another important thing to consider is the species of fish that you plan on keeping in your bowl or fish tank. Some species have feeding, breeding, or cleaning habits that make one substrate better than another for their habitats.
- Design vs. Maintenance: Of course, you should also consider which substrate will give your aquarium the look that you are going for – but the vision that you have for your tank should be weighed against the needs of the fish as well as the maintenance requirements that you’ll be taking on with your choice.
What Is the Purpose of Substrate?
You might be thinking that whatever you put in the bottom of your aquarium is just for looks but the substrate of your aquarium actually performs some pretty important functions. Even a bare bottom can be an acceptable approach to setting up your aquarium as long as you understand what that means for you in terms of maintenance and what that means for your fish.
If you want to have live plants in your aquarium then a bare bottom obviously isn’t going to work for you. If, on the other hand, you want a small and easy to maintain habitat for a single fish then a bare bottom bowl is just the thing. It’s all about finding the combination of options that give you as much of what you want as possible without getting you into anything that you can’t or won’t stick with.
Among the things that you should be thinking about when you choose a substrate for your aquarium are:
- Bacteria: The substrate that you put in your aquarium will be a breeding ground for bacteria. That includes the good bacteria that will help convert leftover food and fish waste into less harmful compounds as well as the bad bacteria that can build up over time and lead to toxic water conditions.
- Habitat: The substrate that you put in your aquarium will not only offer the fish in your aquarium an important element of their environment but also determine what you can and cannot add to that environment in the way of plants and other decorative elements.
- Decoration: Creating an aesthetically pleasing environment inside the aquarium is one of the most important steps in making sure that you enjoy having the tank and its residents as part of your life. Choosing substrate elements that fit in with your overall plan is important to make sure that you can actually do everything else that you want to do.
How Does Substate Influence Aquarium Maintenance?
Once you have decided what the ideal set-up for your aquarium substrate would be, you need to take a step back and consider whether that set-up will fare well under a maintenance routine that you can and will stick with over time. The substrate that you choose will impact the options that you can consider when shopping for filters for your aquarium. It will also influence the amount of work that you have to do during cleanings.
If you don’t use any substrate at all, it will be easy to clean your tank or bowl. It doesn’t matter whether you use a gravel vacuum or do a full water change, the fact that there is nothing in the way means that you’ll have an easy time getting all of the leftover food and fish waste out of your aquarium. At the same time, you have to realize that you’ll see everything on a bare bottom so cleanings will be required more frequently.
At the other end of the spectrum – in terms of complexity of substrate – is the living substrate that you use for live plants. Because this layered substrate creates its own bio-filter, you won’t want to disturb it during cleanings. Your maintenance will consist of partial water changes and filter cleaning. It’s harder to set up but it gives you more options for aquaculture and makes cleaning and maintenance easier.
Both marbles and gravel fall in between a bare bottom and a living substrate—in terms of complexity and in terms of maintenance requirements. We’ll take a look at the specifics of each before we move on to a comparative analysis of the pros and cons of each type of substrate.
Some types of aquarium filters are designed to work best in combination with particular types of substrate while others are able to perform equally well with any type of substrate or no substrate at all. Obviously, if you’re looking to set up a small fishbowl and do 100% water replacements on an as-needed basis then a filter isn’t a concern for you. But anytime you’re looking for a larger set-up—filtration should be something you consider in the planning stages.
When you use a hanging filter such as a canister, you can use any type of substrate that you wish – or no substrate at all. Under gravel filters, on the other hand, require the unique characteristics of a gravel substrate to function.
Under-gravel filters work by drawing waste down into the gravel. The particle size of gravel allows adequate flow and also works to trap the waste in the substrate. Finer substrate like sand can clog the filter. It can also trap the waste in air pockets and lead to the production of smelly Hydrogen Sulphide gas. Coarser substrates like large gravel or marbles can fail to provide under gravel filters with the buffer that they need to work at their best.
Another important element of aquarium maintenance is vacuuming up the trapped waste from your substrate. When you go with a living substrate, you won’t need to perform this maintenance step as part of your routine maintenance. If you go with a bare bottom, you’ll need to perform this task every time the amount of waste on the bottom of the tank gets to be more than what you want to look at.
When you go with a sand or gravel substrate, vacuuming is probably all of the maintenance that you’ll have to do to your tank beyond the water changes you use to maintain water quality. For finer substrates, you’ll need to make sure that you aren’t vacuuming up the substrate. This can be done by stirring the substrate so that it releases the waste and allows you to vacuum it up.
A gravel vacuum makes cleaning gravel easy. When you choose to go with larger particle size for your substrate – such as marbles – you will probably have to do additional cleaning beyond the vacuum to get at all of the waste trapped in the substrate. If you don’t mind extra work rinsing or even scrubbing the substrate during cleanings, then marbles might be the right choice for you.
Pros & Cons of Gravel as a Substrate for Your Aquarium
As we’ve said before, there are so many options available to aquarium keepers that there will never be a single right way or a best way to set up a tank. With that being said, there are plenty of good reasons why gravel is the most common and popular substrate to use in your tank or bowl. Let’s take a look at some of the reasons why gravel is the substrate of choice for aquarium enthusiasts. Once we’ve done that, we’ll take a look at some specific situations where gravel doesn’t work well.
The biggest reason that people prefer gravel for their tanks and bowls is that it gives them a nice uniform look while offering them plenty of choices in color and plenty of flexibility for adding additional features. Gravel is the most versatile option, which is why it ends up being the go-to substrate and the workhorse of the aquarium keeper’s toolkit.
Part of making your aquarium as enjoyable as possible is finding ways to make the maintenance and upkeep something that fits into the rest of your life. If you spend some time thinking about it, you might even come up with a maintenance routine that you actually enjoy. Gravel is a relatively easy substrate to maintain. It works well with any type of filter and it is perfect for use in conjunction with a gravel vacuum.
When you use gravel in your tank or bowl, you’ll be getting a substrate that fits into almost any plan that you have. If you want to try a living substrate, gravel provides a great option for a top layer over the sand and soil that your plants will take root in. If you want to use artificial plants or other decorations, gravel works equally well on its own. You can choose a mix of sizes and colors to design a look and functionality that delivers exactly what you need it to.
When Is Gravel Not the Best Option?
There are some species of fish that won’t do as well with gravel as they will with other substrates. There are some sizes of tank or bowl that and some maintenance routines that will do better with other types of substrates. There are some goals for keeping an aquarium that is better served by other substrates. As we said before, there is no one-size-fits-all solution.
When you choose a quality aquarium gravel, it should be crushed and washed in ways that smooth out the most jagged edges. Even so, some fish species have delicate fins, gills, or barbels that can be torn by any sharp or jagged edges that remain on aquarium gravel. If you’re choosing a species that forages in the substrate, you might want to consider either a finer or a smoother substrate option.
Any substrate is going to collect and hold waste and that waste will break down into chemicals that can lead to a toxic environment for your fish. In small tanks and bowls, this can be as easy as dumping your substrate into a strainer and rinsing it during routine water changes. In larger tanks, you will need a gravel vacuum to clean the substrate. If you want an easier substrate for small bowls and tanks then larger particle sizes might be the way to go.
If you are trying to breed fish then a tank with gravel won’t provide the right substrate for any species that scatter their eggs. In addition to that, it’s important to think about what happens after the eggs hatch. If you’re going to keep the fry in a tank with other fish, larger gaps between particles will give the fry a place to hide. Gravel won’t provide them with the cover they need to stay safe.
Pros & Cons of Marbles as a Substrate for Your Aquarium
Marbles provide a distinct substrate option. They differ from gravel in terms of looks, functionality, and cost. That’s one of the reasons why marbles tend to work best in smaller tanks and bowls. They also offer a great option as a supplemental or decorative addition to gravel or sand substrates. But marbles have drawbacks.
For example, they don’t work well with live or artificial plants unless you take additional steps to anchor them to the bottom of the aquarium.
Marbles don’t deliver the natural look that sand or gravel will but if you’re going for a highly stylized aesthetic for your tank or bowl then marbles might be just the thing to deliver it for you. The larger gaps in between marbles do a great job of trapping waste but marbles are too heavy for gravel vacuums to dislodge so the waste doesn’t get released during vacuum cleaning.
If you’re looking for a smooth and beautiful substrate for a tank that is small enough to make thorough cleanings during each routine water change practical then you should consider marbles. Otherwise, you might want to limit their use to decorative applications in combination with other primary substrate materials.
They have their drawbacks but they also have a look that makes the extra work worth it for many aquarium keepers. If you’re establishing a breeding tank then marbles provide advantages that make all of the challenges that come along with them more than worth it.
The egg-scattering habitat and hiding places that they provide make them ideal for breeding tanks. Their smooth edges make them a great option for species with delicate fins, gills, or barbels.
There are many options to choose from when you’re selecting the substrate for your aquarium. Whether you’re setting up a small bowl for a single fish or a large fish tank with powered filters to provide an environment for diverse species, you need to consider what will work best for the fish and for you. At the end of the day, figuring out what you and your fish will enjoy the most is what it’s all about.
Taking advantage of what gravel does best will give you a great substrate for the vast majority of aquarium applications. At the same time, there isn’t a single right way to do it. You might feel that marbles provide a better option. This is especially true when you are setting up a smaller tank or bowl and have the ability to thoroughly clean the substrate during routine water changes.