Why does cloudy water appear after maintenance?

Cloudy water after maintaining the aquarium filter indicates a serious issue is occurring. Essential bacteria that break down fish waste are being disturbed. This allows ammonia to accumulate rapidly. Left unattended, the fish could die from poisoning within forty-eight hours. Immediate water testing and supplements may be needed. I have saved many tanks from this disaster.

Nitrifying bacteria colonies adhere to the surface of filter media. The cleaning process removes a considerable portion of this bacteria. The bacteria remaining are incapable of immediately processing waste. Thus, a bacterial bloom further competes for existing resources. Considered an "out of balance" system, the ammonia level may rise to over 0.5 ppm in the short term. During this period, fish exhibit signs of distress, characterized by increased gill movement.

How to avoid cloudy water: do not clean biological media in tap water; contain the exposure time to less than 30 minutes; add bacterial supplement when filter is restarted; keep ambient water temperature fairly constant. By doing these things you will keep the nitrifying bacteria alive.

For three days after completing the maintenance, check your water parameters and test for ammonia twice daily using liquid test kits. Strip tests are too approximate and do not provide the resolution necessary to accurately gauge the recovery that will occur. Record the results, and you will notice the water returns to crystal clear when the colony of bacteria has righted itself. Healthy filters should hold up indefinitely.

Read the full article: Aquarium Filter Maintenance: Essential Care Guide