Why does cloudy water persist despite filtration?
Written by
Hoang Long
Reviewed by
Prof. David Walsh, Ph.D.If you are left with persistently cloudy water in your filtered aquarium, even with the filters fully operational, there is a reason. This is likely due to bacterial activity, inadequate waste removal, or poor husbandry practices. If you know the correct cause, you will learn how to rectify the situation. If the water appears clear but is obviously contaminated with bacteria, biofiltration is suboptimal. You must address mechanical problems and eliminate bacterial activity simultaneously.
Bacterial Blooms
- Overfeeding creates excess organic matter feeding bacteria
- New tank syndrome during nitrogen cycle establishment
- Solution: Reduce feeding by 50% temporarily
Insufficient Mechanical Filtration
- Filter media too coarse to capture fine particles
- Clogged media reducing effective flow rates
- Solution: Add filter floss or polishing pads
Substrate Issues
- Disturbed gravel releasing trapped debris
- Anaerobic pockets producing cloudy gas bubbles
- Solution: Vacuum substrate thoroughly weekly
If the cloudiness persists, consider replacing the mechanical filter floss with a fine filter floss that targets particles down to 5 microns. This will act as the final line of filtration before the water returns to your tank. In canister filters, you can add polishing pads in their own chamber. Remember to replace it weekly before it becomes fully saturated!
Adjust feeding practices immediately to minimize organic waste. Use a daily ration container to portion out food. Remove uneaten food within five minutes during all feedings. Consider fasting from fish one day a week to initiate a biological reset. All of these changes significantly reduce the food supply for bacteria.
"Clean substrate properly during water changes. Use gravel vacuums that pick up debris without stripping the last layer of substrate in the process. Work methodically back and forth over every inch of the tank's floor. On sand substrates, hover unnaturally high above at a slight angle to pick up debris without stripping significant amounts from the substrate above. Removing waste should be easy. If it's not, you're doing it wrong.
Distribute water flow evenly through your aquarium. Point filter outputs are located in areas where the flow will circulate the water in a circular motion, and powerheads are used in large tanks to eliminate all dead spots. Move debris constantly toward areas where filter intakes will remove it. Balanced circulation prevents particles from settling.
Pay attention to the water parameters to pinpoint the issue. Test for ammonia, nitrites, and nitrates on a weekly basis. In many cases of bacterial blooms, it is common to see an ammonia spike below 1ppm or so. Continuing high nitrates indicate inadequate water changes. The parameters and their imbalances need to be addressed (specifically anything that prevents permanent clarity).
Read the full article: Understanding Aquarium Filtration Systems
