How to Slow the Flow in Your Aquarium

Previously, we discussed the importance of filtration for fish tanks because it cleans up debris particles, grows beneficial bacteria, and helps create water movement and surface agitation for improved oxygenation. It is possible that your aquarium filter is too powerful and is producing too much current for your fish. Some fish are large and have flowing fins. Others are smaller and were born from slow-moving waters. They are not built to handle high volumes of water. Perpetually fighting against fast flow can cause your fish to get whipped around the tank, start hiding in shelters, and potentially develop illnesses from the constant stress. If you own a betta, goldfish or cherry shrimp, these are some of the techniques that can be used to reduce current in your aquarium.

Use a filter with slow flow

The simplest way to reduce the current is to not use too much filtration in your aquarium. Sometimes people install multiple filters to ensure a clean tank. Other times, newcomers to the hobby pick up an all-in-one aquarium kit and don’t realize that the default filter is too strong for bettas and other slower fish. Do not be afraid to reduce the size of your filter if your fish seem to be struggling.

For gentle flow, our favourite type of filtration is a sponge filter that uses a smaller pump such as the USB Nano air pump. Its coarse foam is perfect for straining debris from the water without sucking up any baby fish, and the bubbles create good surface agitation to ensure your fish get enough oxygen. Some air pumps come with a flow dial to lessen the air pressure if needed, but if the pump isn’t adjustable, you can also add an air valve outside of the fish tank to reduce the amount of bubbling. You may prefer another type of filter such as a hang-on back or canister filter. If the pump has an adjustable knob or switch that allows you to adjust the flow rate of water entering the aquarium, this will be an option.

Sponges offer gentle flow that won’t harm your fish fry or bettas and other nanofish.

Reduce the Output

You can use many methods to divert, baffle, or block the water flow from the filter to lower the water pressure. To reduce water pressure, you can use an aquarium’s internal filter or canister with an output spout. You can aim the output at the aquarium’s water surface or back wall. The current drops if the water “bounces off” the wall or surface. A prefilter sponge can be placed on the output. The coarse sponge will absorb most of the water’s energy, but still allow the water to flow into the tank. If the water flow is strong enough to knock off the pre-filter sponge, try securing it by propping the pre filter sponge against a wall or sturdy aquarium decoration. A spray bar can be attached to some canister filters to help reduce energy loss when water passes through a row. Spray bar holes can be directed towards the aquarium’s back wall in order to decrease the current.

Affix a pre-filter sponge to the output filter to release water pressure.

If you have a hang-on-back filter with a waterfall output, there are several filter baffle techniques that can help reduce the flow while still allowing some surface agitation. Cut a block of sponge to fit the opening of the waterfall. Attach craft mesh to the waterfall opening by using string or zip ties. Some people recommend attaching a soap dish container with suction cups to the aquarium wall under the waterfall. To dampen the flow, you can add foam, decorative marbles, or moss balls to the soap dish.

Finally, try placing live plants, hardscape, or fish tank ornaments in front of the filter output or underneath the waterfall to help block the force of the water. More plants and decorations added throughout the rest of the aquarium will also break up and hinder the water movement in the tank. Depending on your setup, you may be able to combine several of these methods to decrease the current and give your fish the stress-free environment they need.

To reduce the flow, place a soap dish, plants or decorations underneath the waterfall of your hang on-back filter.

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