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. However, is it possible your aquarium filter is overly powerful and produces current that is too strong 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 that has slow flow

You can reduce current by not using too much filter in your aquarium. In their quest to have the cleanest tank possible, people sometimes install multiple filters or get oversized filters that are meant for much bigger fish tanks. 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. If you see your fish struggling, don’t be afraid to downsize your filter to better accommodate their needs.

A sponge filter with a small pump, such as the USB nano-air pump, is our favorite type of filter for gentle flow. The coarse foam can be used to strain debris out of the water, without sucking up baby fish. Additionally, the bubbles provide good surface agitation so that 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 can also use a different type of filtration such as a hang on-back or canister filter.

Sponges are gentle and won’t cause harm to your fish fry, bettas or other nano fish.

Reduce the Output

To reduce water pressure, there are several ways to block, redirect, or baffle the water coming out of the filter. 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. Another idea is to put a prefilter sponge 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. Some canister filters let you attach a spraybar to the output to reduce the energy loss as the water is dispersed through a series of holes. To lessen the current even more, aim the spray bar holes toward the back wall of the aquarium.

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

You can use filter baffles to help reduce flow and allow surface agitation with your hang-on-back filter. Cut a block of sponge to fit the opening of the waterfall. Another idea is to attach craft mesh across the waterfall opening using zip ties or string. Some people recommend attaching a soap dish container with suction cups to the aquarium wall under the waterfall. To further dampen the flow of water, add some foam, marbles, or moss 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. You may be able combine these methods depending on the setup to reduce the current and provide your fish with the stress-free environment that they require.

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

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