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How to add substrate to your established fish tank

So you want to add more to the substrate to your established aquarium but don’t know the correct process to do so.

This guide at Aquarium Blueprints will provide some tips will make the process much easier for you.

Should You Remove Your Old Substrate?

Thinking about replacing your old substrate with a new one? We highly recommend you don’t.

This is because, aside from maybe your filter media, the sand, gravel, peddle and/or whatever you are using as a substrate are where most of your beneficial bacteria are living on. For the uninformed, these microorganisms covert ammonia to nitrite and then nitrite to nitrate. Both ammonia and nitrite, which are products of food and wastes, are toxic to the fish in your aquarium.

If you remove your old substrate, you are essentially killing off a large population of your beneficial bacteria. Even if you add in the new substrate, it will take some time for the population to be at the same level as before. This will leave you with an un-cycled tank that could results in spikes of ammonia and nitrite.

So, instead or replacing your old substrate, we recommend topping it off with the new substrate. That way, you won’t have to worry about losing any bacteria.

If you are using a substrate made specifically for plants, we recommend using root tabs to replenish to nutrients needed instead of replacing the soil.

Removing fish and decorations

As a precaution, you might want to think about removing fish before topping off your substrate. Doing so will prevent stress and potential injury.

With that said, top and middle dwelling fishes should be fine if you are careful enough in adding your new substrate. For bottom dwelling fish and species, you might be better off removing them from the tank until you are done.

If any decorations are in your way, you should remove them as well. Keep in mind that beneficial bacteria also live in the decorations. So, if you decide to remove them, it is best to place them if a bucket or container with used aquarium water (you can also use your tap water as long as you use a dechlorinator beforehand as well).

Should you lower the water level?

So, should you lower your water level before adding in your new substrate? It depends on your water level.

If your tank is filled to the brim with water, then you should take some water out before adding in your new substrate. This is because the new substrate will raise the water level, which may cause an overflow if you aren’t careful enough.

With that said, we don’t really recommend doing a large water change (which we considered to be above 50 percent), as it could significantly change your water parameters. You fish could become stress and sick as a result.

Water Bottle Method

To add substrate to an existing tank, we recommend using the water bottle method. To begin, make sure you clean both the water bottle and your new substrate (you can find out how to clean your substrate here).

The next step is to fill the bottle with the new substrate.

Afterwards, put your thumb on the top part of the bottle, but leave a little opening, and then dip the bottle into your tank from the bottom side on up. What you are trying to do here is to fill the rest of your bottle with the aquarium water while not letting any of the substrate get out at the same time.

Once the bottle is completely filled with both your substrate and aquarium water, cover the top of the bottle completely with your thumb.

Bring the bottle over to the area of the tank where you want to put your new substrate on.

Finally, you can remove your thumb from the top of the bottle and then pour the substrate down to your desired location.

Repeat the process for the rest of your new substrate.

You can find a helpful video on this method from the Arowana Planted Tank channel on YouTube below:

The water bottle method ensure that you don’t have to lower the water level in your tank and is generally less messy. Not to mention that this way is less stressful for your fish than simply pouring all your substrate in at once.