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How to Convert a Saltwater Tank to Freshwater (Is it Really Possible)?

Sometimes you start something and then later change your mind. I’ve run into this myself in the aquarium hobby regarding whether to keep a saltwater or freshwater tank. Perhaps you find your saltwater tank just too difficult to maintain and are now thinking of converting it to a freshwater tank. Is this even possible?

A saltwater tank can be converted to freshwater. In order to do this, the saltwater will have to be replaced with freshwater, the filtration medium will need to be replaced, and the substrate will have to be replaced if it is a crushed coral or other type of substrate that increases PH in the water. 

You can add decorations as well, especially if they’re some type of porous rock. Unfortunately, just emptying out the saltwater and replacing with freshwater isn’t good enough. Unless you just want a tank with water, but I’ll assume you want to add some freshwater fish eventually!

This process is very straightforward, and in this article, I will help you get through the changeover successfully. So if you’re ready to learn more, then let’s get to it!

Emptying Your Saltwater Aquarium

The first step in this process is to empty the saltwater out of the tank.

The saltwater is no good for a freshwater tank so you can go ahead and pour it down the drain.

Make sure your filter, heater, powerheads, and anything else electric is unplugged before proceeding.

Instead of using a pail and scooping the water out, you can hook up a pump and hose that will reach from your tank all the way to the sink for draining.

These pumps and hoses are the water change or vacuum gravel cleaners like this one on Amazon. If you have one already, then great! But if not, they you should invest in one. They’re super cheap and very handy for performing weekly freshwater changes.

Next Step after Emptying the Water from the Saltwater Tank

Now that all the water is gone and everything is unplugged, the next step would be cleaning out the filter and exchanging the filter medium with new sponges and charcoal – if you want to run with charcoal.

You can also use bio balls or something similar to offer beneficial bacteria another place to grow in your filter – if you have room, of course.

Next step is to clear out everything on the bottom of the tank and either give it a good rinse and or get rid of it.

If you are wanting to reuse anything, make sure to give it a good rinse and maybe a scrub to take off anything encrusted.

As far as getting rid of anything, if you happen to have coral sand that should be replaced by sand safe for freshwater or aquarium gravel.

Coral sand will raise the PH in your freshwater tank and could be harmful to the fish. There are some freshwater fish that prefer higher PH levels such as guppies and mollies.

Your next thing to do would be to give the inside of the aquarium a wipe down with some vinegar and water.

What to do after Everything is Removed from the Saltwater Aquarium?

Now that you have everything out of your saltwater aquarium, you can now start calling it your freshwater tank.

It’s time to start putting your freshwater tank together.

Before you do anything else, right now you have the opportunity to change out any padding you might have between the tank and stand. Over time these pads can become compressed and don’t provide the absorption they once did when brand new. I know a lot of people don’t use padding between the tank and stand however, it is definitely worth checking into, especially for very large tanks.

Go ahead and put your new substrate in the tank and then fill it with water.

Once that is done, you can turn on the filtration and heater to begin the Nitrogen cycle.

If you are in a hurry to put fish in the tank, I would recommend purchasing a bottle of biological enhancer. It’s basically beneficial bacteria in a bottle.

Be aware though, that using a bottled, beneficial bacteria isn’t he same as letting the tank run through the Nitrogen cycle. It’s a temporary fix that is somewhat unstable.

If you do go this route, I would recommend not having any charcoal in your filter. You don’t want anything filtering out the bottled beneficial bacteria.

Still keep your fish quantities to a minimum if you do this. Once your tank is cycled properly and the Nitrite, Ammonia and Nitrate levels are where they should be, you can stock up the tank.

What Happens if You Don’t Clean All of the Saltwater Out of the Tank?

If you plan on putting freshwater fish in the tank, then you must clean out all the salt. It’s a lot of work but it needs to be done to have a successful freshwater tank.

If by chance you were interested in a brackish tank, you could technically empty out most of the water and refill with freshwater. The amount of salt still in the substrate and filtration might be enough to run a brackish tank.

That might be the route to go if you’re interested in keeping fish that most people don’t have.


In conclusion I just want to point out that yes, obviously you can convert a saltwater aquarium into a freshwater tank. You just need to clean all the saltwater remnants out of the tank and then refill.

It would be great if you could just empty the saltwater out and refill with freshwater, but you can’t. The freshwater fish probably wouldn’t survive as there would still be salt in the substrate and filtration.

As I mentioned in the previous section, you could go with brackish fish if you wanted to but this article is about converting to a freshwater tank.

Something else to consider is that a bottle of biological enhancer is not the same as a tank that has cycled. If you put fish in early, I recommend using the enhancer weekly and keep a close eye on the water parameters (nitrite, ammonia, nitrate).

Hopefully, this article has been helpful to you. Thanks for reading and good luck with your aquarium change over!

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