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. Is it possible that your aquarium filter produces too much current for your fish? Some fish have long, flowing fins or are small and not designed to handle large amounts of water. Fighting against the flow of water can lead to fish getting tossed around, hiding in shelters, or developing illnesses. 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. Some hobbyists buy an all-in-1 aquarium kit, but don’t realize the default filter is too strong to support bettas and slower fish. If you see your fish struggling, don’t be afraid to downsize your filter to better accommodate their needs.

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 ideal for straining any debris from the water and not sucking up any baby fish. The bubbles also create good surface agitation to ensure that your fish get enough oxygen. You can adjust the pressure of an air pump by using a flow dial. If the pump doesn’t have a flow dial, you can add an external valve to reduce bubbling. If you prefer to use another type of filtration like a hang-on-back or canister filter, check to see if it has an adjustable switch or knob that allows you to modify the flow rate of the water entering the aquarium.

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

Reduce the Output

To reduce water pressure, there are several ways to block, redirect, or baffle the water coming out of the filter. To dispel some water pressure in an aquarium that has an internal filter or canister, aim the output towards the surface of the water or against the wall. When the water “bounces” off the surface or wall, it loses kinetic energy and the current decreases. 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. The pre filter sponge can be secured against the aquarium wall or strong aquarium decorations if it is damaged by water. 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. 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. You can cut out a block of sponge that fits the width of the waterfall and stuff it into the waterfall opening. Attach craft mesh to the waterfall opening by using string or zip ties. Many people also recommend using a soap dish container with suction cups and attaching it to the aquarium wall right under the waterfall. To dampen the flow, you can add foam, decorative marbles, or moss balls to the soap dish.

To help reduce the water pressure, you can place live plants, hardscape or fish tank ornaments either in front of or under the waterfall. Adding decorations and plants to the aquarium will cause the water to break down and slow down. Depending on the configuration of your aquarium, you might be able to combine multiple of these techniques to lower the current and provide the fish with the stress-free environment they desire.

Place a soap dish or other decorations under the waterfall of the hang-on-back filter. This will reduce the flow.

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