Can water movement be too strong in aquariums?
Written by
Hoang Long
Reviewed by
Prof. David Walsh, Ph.D.The movement of the water in your aquarium should balance oxygenation with swimming comfort for your fish; too much current is exceedingly trying to those species that are inhabiting the still waters of lakes and pools; it not only disturbs them, but uproots your plants and blows the sand and mud all over your tank; whilst, on the other hand, too slight a circulation allows impurity to become collected and the water to become deoxygenated.
Too Strong
- Fish struggle against current or hide constantly
- Plants uproot or show torn leaves
- Substrate blows into bare spots
- Food gets swept away before fish eat
Too Weak
- Debris accumulates in corners
- Algae grows on slow-moving surfaces
- Fish gasp at surface
- Uneaten food decomposes on substrate
Ideal Flow
- Gentle plant movement without uprooting
- Fish swim comfortably throughout tank
- Waste moves toward filter intake
- Surface shows slight ripple without splashing
Target "4-5 times tank volume hourly" for optimal circulation. Multiply tank gallons by 5 to arrive at the gallons-per-hour figure. A 20-gallon tank would need a total flow of 80-100 GPH. Add all the pumps and filters to get this figure for the tank. More than eight times the volume, and we are asking for trouble.
Adjust flow with simple modifications: Attach spray bars for even distribution of concentrated outflow. Point filter returns towards the surface rather than straight into the water. Add aquarium-safe sponges to nozzle output to lower the outgoing velocity. Use decorations that break the current to create moderation in flow; I've used driftwood to somewhat shield bettas from my strong filters.
Check the fish for their current stress signals every day. Some companies do not venture into strong areas; for example, angelfish will fail to hold against the current, and guppies will get blown along the substrate. You should immediately reduce the current if the fish start going with the current in this way. If they are relaxed with the flow, your circulation is probably correct.
Balance flow with your specific tank needs. For planted tanks, a gentle surface disturbance helps retain carbon dioxide (CO2) in the water. Reef tanks thrive with varying levels of water movement depending on coral species. Use equipment as necessary to suit your inhabitants rather than following rules laid out in user manuals. Your aquatic ecosystem will thrive!
Read the full article: Understanding Aquarium Filtration Systems
