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 have long flowing fins and small sizes. Fighting against the flow of water can lead to fish getting whipped around, hiding in shelters, or developing illnesses. So, if you own a betta fish, goldfish, cherry shrimp, or other slow-swimming animal, consider implementing one of these techniques to reduce the current in your aquarium.

Use a slow-flow filter

You can reduce current by not using too much filter in your aquarium. People often install multiple filters in an effort to keep their tank clean. Some hobbyists buy an all-in one kit, but don’t realize the default filter is too strong to support bettas and slower fish. Don’t be afraid if you notice your fish are struggling to get the filter downsized to meet 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. Its coarse foam is ideal for straining any debris out of the water without sucking in any baby fish. Furthermore, the bubbles create excellent surface agitation to ensure enough oxygen is available to your fish. Most air pumps have a flow dial that can be used to lower the pressure. However, if the flow dial is not available, an air valve can be added to the tank to reduce bubbles. 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 are gentle and won’t cause harm to your fish fry, bettas or other nano fish.

You can’t confuse the output

You have many options to redirect the water from the filter, either to stop it or to make it more difficult. If you have a canister or internal filter with an output spout inside the aquarium, try aiming the output towards the water surface or the back wall to dispel some of the water pressure. The current drops if the water “bounces off” the wall or surface. Another option is to place a prefilter sponge over the output. The coarse sponge will dissipate most the water’s heat while still allowing water to enter your fish tank. The pre-filter sponge can be secured against the aquarium wall or strong aquarium decorations if it is damaged by water. Finally, some canister filters allow you to attach a spray bar to the output so that the water loses energy as it’s dispersed through a row of holes. Spray bar holes can be directed towards the aquarium’s back wall in order to decrease the current.

Attach a pre-filter sponge or spray bar onto the filter output to dissipate the 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. 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 dampen flow further, place decorative marbles or foam in 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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