Replacing the Substrate in a Saltwater Tank


Fox-faced Rabbitfish (16444109145)It is possible to replace substrate in a saltwater tank, but it’s not recommended if the current substrate isn’t causing a threat to aquatic life. Disrupting the substrate may cause bacteria, ammonia, or particles to disrupt the delicate balance of the tank. Still, if the substrate is no longer a benefit to the tank, it must be swapped for something new.

Selecting a New Substrate

Sand substrate is known to cause nutrient levels to rise over time, making it necessary to replace sand every 2-5 years. Sand substrates collect detritus, which is why most saltwater tank enthusiasts regularly vacuum their sand beds. If you don’t have a vacuum, you may be interested in one of the other saltwater tank substrates available. These include: aragonite, crushed coral, coral sand and crushed seashells. Aragonite is an especially good substrate option because it helps to regulate pH balances.

Clean the New Substrate

If you chose sand substrate for your saltwater aquarium, you may not want to clean it. Oftentimes, cleaning sand substrate reduces the particle size in the sand bed. For all other substrates, fill a bucket no more than half-full with the substrate. Then, fill the bucket with an equal amount of water. Mix the substrate into the water with your hands, allowing the water to become cloudy with any dust or dirt that may be on the substrate. Continue to fill the bucket with water, allowing the cloudy water to spill over the sides. When the water is clear, the substrate is clean.

Changing the Substrate

Because a saltwater tank’s substrate contains a large amount of nitrite and ammonia, it’s not recommended to completely remove all of the previous substrate in a single day. Instead, remove half the substrate one day and the other half in a couple weeks when things have calmed down in the tank. Begin by turning off your pumps. You can use your hands or a scoop to pull out the old substrate. Alternatively, if you want to ensure the tank stays clean during the process, you can use a hose to syphon out the old substrate. Place the old substrate in a bucket if you plan to keep it. Otherwise, throw it out.

Adding the New Substrate

Gravel substrate can be lowered into the tank using your hands or the same scoop you used to remove the old substrate. Spread it out once you’ve reached the bottom. Sand substrate, and other lightweight substrates, cannot be lowered to the bottom. These substrates should be sealed in a freezer bag. Lower the sealed bag to the bottom of your tank and then gently open it and pour the lightweight substrate along the bottom. Some particles will still be kicked up into the water, but for the most part, this method should keep things settled.

Allow Everything to Settle

After you’ve added your new substrate, the tank is going to be rather cloudy. Before reintroducing fish, you’ll want to allow all the substrate to settle and the water to clear. This can take as little as two hours, but up to a full day. You can speed up this process by replacing 20 percent of the water. Once the tank is clear, turn on your pumps, add your décor and reintroduce your fish.

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