Aquarium Substrate: 8 Things You Should Know (For Beginners)

Aquarium substrate is this material you put in a tank mostly for aesthetic purposes, however, aquarium substrate also serves other purposes such as providing a home for beneficial bacteria, habitat for fish, and the like.

This begs several questions, can you use aquarium substrate? Does aquarium substrate go bad? How often should these be changed?

Can I Use An Aquarium Substrate?

Yes, you can use aquarium substrate. Aside from being used primarily for aesthetic purposes, these provide several benefits to an aquarium and its inhabitants as well. This applies to both planted tanks and fish-only tanks.

“Can I use an aquarium substrate in my tank?”, this is often wondered by those who are new to the whole aquarist hobby since they’re not certain if these are safe for their tanks. The answer to this question would be yes—aquarium substrate is safe to use in a tank but only if used in appropriate conditions.

So what do we mean by appropriate conditions? Well, several aquarists put aquarium substrate in their tanks since these provide benefits to it, however, it’s important to note that aquarium substrate wouldn’t be necessary for other kinds of tank setups.

Aquarists who would put aquarium substrate in their tanks would be the ones that own either a planted tank or a typical fish-only tank. A typical fish-only tank would exclude fish fry and injured fish. With that being said, the kinds of fish tanks you should avoid putting aquarium substrate in would be grow-out aquariums and hospital tanks.

It wouldn’t be recommended to have aquarium substrate in a grow-out tank because fish fry can get lost in them and you might accidentally end up vacuuming them out of the tank or getting rid of them when conducting water changes to your tank (this kind of scenario would most likely happen in grow-out tanks since this kind of tank needs to be cleaned often).

Next, it’s a no-brainer for aquarists that hospital tanks and quarantine tanks should always be kept clean to prevent infecting sick fish. Several types of aquarium substrate have a possibility of having pathogens which is why it should be avoided in both hospital tanks and quarantine tanks.

Does Aquarium Substrate Go Bad?

No, the aquarium substrate itself doesn’t go bad, however, if the condition of your tank is poor, then it could affect your aquarium substrate, and in turn, worsen the condition of your tank.

Aquarium substrate, no matter what material is used, won’t go bad. Even though aquarium substrates don’t go bad, specific substrate materials need to be replaced over time. Before we delve deeper when it comes to replacing your aquarium substrate we must determine first how your tank’s condition can affect your aquarium substrate.

Poor tank conditions that are most likely caused by neglect, such as inadequate water changes, overstocking of fish, clogged/dirty filters, food that wasn’t eaten by fish, decaying plants, and dead tank inhabitants will affect your aquarium substrate.

If these manage to get into the aquarium substrate then that would most likely result in:

  • Increased nitrate release
  • An extreme drop in oxygen levels
  • Production of hydrogen sulfide
  • Wrong kinds of bacteria will start to grow

Not only would these cause trouble for your aquarium substrate but also would affect other aquarium accessories such as a filter. Once this happens, the issues inside the tank would escalate. Luckily this can be prevented by making sure your tank is cleaned regularly.

How Often Should You Change Your Aquarium Substrate?

You should change your aquarium substrate after three to four years, take note that this is merely an estimate. How often you should change your aquarium substrate would largely depend on your tank condition and its setup.

If your tank doesn’t have a decent filter that can remove the impurities in your tank then you’re going to have to change your aquarium substrate a lot more often than usual. Why is that so?

Well, it’s not a good idea to have dirty aquarium substrates since these would worsen your tank’s condition, so that’s why you’ll be prompted to change them a lot more often.

If you do have a decent filtration system installed in your tank, that would lessen the frequency of you changing your aquarium substrate.

Aside from aquarium accessories, your aquarium substrate would need to be changed if you’re experiencing the following:

  • If you have a planted tank and need a soil substrate but your substrate isn’t the right material
  • If you own bottom-feeding fish and would like to prevent them from getting injured from gravel (this type of material is too sharp for bottom-feeding fish and would cut them once they come in contact with the fish)
  • If you wish to combine two different substrate materials

Overall, if you take good care of your tank and have decent filtration then you wouldn’t need to change your aquarium substrate too often. Instead, you can change the aquarium substrate once three or four years have passed.

How Do I Change The Substrate In My Established Aquarium?

You can change the substrate in your established aquarium by moving your fish in a holding tank, scooping out the old substrate and placing them in a bucket, vacuuming the debris that’s left in the bottom of the tank, and then adding the new substrate inside the tank.

When changing the substrate in your established tank you must follow several steps:

  • Planning
  • Proper timing
  • Setting up a holding tank for your fish
  • Moving the fish
  • Replacing the current substrate
  • Test the water after three days from the day you changed the substrate

Planning is an important step since changing substrate in an established tank would be a tedious process, so you must make sure that you have all the materials for this. This would include the holding tank for your fish, new gravel, nets, siphon, buckets for the old substrate, a clean cup to scoop out the substrate, and water treatment.

When it comes to the holding tank, you must plan what alternative you’re going to have if you don’t have the budget for it. Alternatives would include a 10-gallon tank or a 5-gallon clean bucket (make sure that this is void of chemicals/detergents).

Moving on to the next step, you must time the changing of substrate properly. Avoid changing the substrate right after you’ve cleaned your filtration system. Bear this in mind since this would allow enough time for the bacteria in the filter to stabilize. Next, test your water for ammonia and nitrate.

If you see that there are levels of ammonia and nitrate in your tank, you must address that and lessen that level to zero. Then, avoid feeding your tank inhabitants the day before changing the gravel since this would prevent them from releasing waste in the tank.

On the day of changing the substrate, you have to set up the holding tank for your fish. Grab your new substrate and rinse them in water (make sure the water becomes clear before you stop rinsing the substrate). Then, set up the holding tank near your main aquarium to make transferring (of the fish) easier.

Once the fishes have been transferred, proceed to turn off the filter in your main tank. For the next step, you must proceed with a bit of haste so that the filter would only be turned off for a short time.

With the siphon, siphon water that would fill the holding tank (two-thirds would be the right amount). Proceed to remove all the decorations in your aquarium and transfer them to the holding tank; this is to make way for the preservation of beneficial bacteria on them.

Use the net and transfer them directly to the holding tank. To avoid having your tank inhabitants from jumping out of the holding tank, make sure to cover the top of the tank itself. You can turn the filter back on once you add treated water to the main tank.

Before you add the substrate, make sure that the treated water won’t fill up the main tank since you need space for your decorations. The next step would be to scoop out the old substrate inside the tank and put them in the bucket. Vacuum the leftover debris inside the main tank and then add the new substrate.

After adding the new substrate, you can now add the decorations; lastly, you may transfer all the fish back to the main tank. To prevent your tank inhabitants from becoming stressed you may pour some stress coat in the tank.

Take note:

  • On the first day of feeding fish, make sure to feed them less food than usual. You may feed them a normal amount the day after.
  • Ensure that your nitrate and ammonia levels won’t spike by monitoring them regularly.
  • Check your tank for ammonia after three days (from the day you changed the substrate). Do this process twice. Wait for a week before you do the third attempt (only do this if the ammonia levels in your tank are still zero).
  • If you spot an ammonia spike in your tank you may test the tank water frequently and conduct water changes until the ammonia and nitrite spike is gone.

Can I Put Sand Over Substrate?

Yes, you can put sand over substrate. Layering different kinds of substrate materials are usually done to enhance the benefits of each material.

Adding sand over another kind of substrate material isn’t necessary since this would depend on your preference. Either way, your tank still reaps the benefits from the substrate you add to the tank.

If you’ve finally decided to put sand over your other substrate, make sure that this is what you want. Remember, it would be a tedious process to change your substrate once you’ve mixed them.

Moreover, the best method in mixing sand with other (coarser) substrates would be putting a layer of stones in between the sand and the other substrate material.

Can I Mix Gravel And Plant Substrate?

Yes, you can mix gravel and sand substrate. Gravel is a great combination for plant substrate since this would help keep plants planted down in the tank and the roots would still be able to spread beneath the substrate.

While you can mix gravel with a plant substrate, it wouldn’t be the best substrate material to be used in a planted tank. Why so? Well, plants can’t get any nutrients from gravel so it would be best to choose a different kind of substrate to mix it with; something that would provide benefits to plants.

Sand Substrate V.S. Gravel



  • Affordable
  • Sand substrate is safe for bottom-feeding fish.
  • Debris won’t get trapped in the sand since these would stay on top of it.
  • There are lots of varieties when it comes to sand substrate (in terms of color and size).


  • Sand can get into filters and pumps and damage them.
  • These don’t provide any nutrients to plants.
  • This type of substrate isn’t ideal for planted tanks.
  • Sand tends to wound up in the water column.
  • There’s a possibility that anaerobic areas can form in the sand substrate, in turn, this would spread ammonia in the aquarium.



  • Gravel allows water to pass through it and this prevents the formation of bacteria and amoebas in the substrate itself.
  • Aquarium mold accumulation would be prevented if you have gravel as your substrate.
  • Gravel won’t block your filters.
  • Affordable.
  • Gravel won’t wound up in the water column since they’re too heavy to be moved.


  • Debris would most likely get trapped in gravel.
  • Gravel needs to be cleaned and vacuumed regularly to prevent debris from building up.
  • Gravel is harmful to fish, especially bottom-feeding ones as these tend to cut them.
  • Gravel doesn’t provide any nutrients for plants.

Aquarium Substrate

CaribSea Eco-Complete Planted Aquarium Substrate, Seachem Flourite, and Pisces Midnight Pearl Aquarium Gravel are some of the best aquarium substrates in the market.

The first two substrates aforementioned are for planted tanks while the last substrate is for freshwater tanks. All three substrates are highly rated in Amazon which confirms that these are quality products that are bang for the buck.

Check these out by visiting the links below: