Generally speaking, there is no right or wrong time to change your aquarium substrate. When you feel it is no longer serving its purpose, you can change it.

Whether it is because it is no longer aesthetically pleasing to you, because you might want to have nicer or carpet-forming plants, or for any other reason, it is up to you to determine when you want to change your substrate.

Is it very complicated to change the aquarium substrate?

Technically, it is not complicated. However, it is a long process because there are no two ways about it. If you want to change the substrate of your aquarium, you have to empty it and start the entire aquarium over. It is almost exactly like the process of moving an aquarium.

The first thing to do is to store your aquarium water. You will therefore need to siphon the water out of your aquarium to empty it completely. Try, however, to keep it in containers, buckets, or water bottles so you can reuse it immediately afterward. You will remove about 10 or 20 liters of water, net your fish, shrimp, and snails, and put them in either a bucket or a temporary aquarium, such as a plastic bin.

Be careful, however: if they are tropical animals that need warm water, you must put a small heater in this temporary tank, and meanwhile, you can continue working on your aquarium.

The next step consists of turning off your heater and filter, and removing all technical equipment from the aquarium.

You must also remove rocks, driftwood, decorations, as well as the plants from your aquarium. If you want to reuse the plants, that is perfectly possible. You just need to gently uproot them and then place them, like your fish, in a small basin with aquarium water on standby while you perform your change.

Then continue to empty the aquarium as much as possible. Once you reach the substrate layer, you can use a shovel and bucket to remove the aquarium substrate. You can use a small gardening trowel, for example, or a small glass or bowl to remove the substrate. Rinse your aquarium to remove any small bits of dirt that may have remained. Finally, put your aquarium back in place and add the substrate of your choice. Replace your decorations, branches, roots, etc., and plant or replant the plants you wish to have.

You can also start with a new planting scheme without any problem. Once you have finished decorating, replace your technical components without plugging in the filters, heater, etc. Fill your aquarium with the water you siphoned and stored in bottles or containers.

Obviously, you will need to top it off because you will have lost a little bit of water in the substrate. After that, you can plug your filter, heater, etc., back in and wait for the water to reach the right temperature. Finally, put your fish back into your aquarium, and you are done.

Conclusion

As you will have understood, the process is not simple, especially if your aquarium is large, but there are no two ways about it. This is the only way to change an aquarium's substrate, naturally depending on the size of your aquarium and what you want to achieve.

If, for example, you are doing aquascaping, it will take more or less time. On a nano aquarium under 40 liters, it will take about half a day, but it can take up to two days for a very large aquarium. So, do not worry about your fish or invertebrate population. During that time, you just need to leave them in their aquarium water with a small heater. Do not feed them while you are performing this operation, and you can keep them temporarily like that for a few hours in an aerated container (with an air stone); if the operation lasts longer, provide a filtered temporary tank.