The most dangerous water change mistakes are changing too much water, using untreated tap water, mismatching temperature, and cleaning the filter the same day. Learn what causes fish deaths after water changes and how to prevent them.
Cloudy water after a water change is usually harmless and clears in 24-48 hours. Learn the two main causes - substrate particles and bacterial bloom - and when to actually worry.
For most home aquariums, change 20-25% of the water weekly. This guide explains the right percentage based on tank size, stocking level, and how to avoid shocking your fish.
Change water when you see cloudy water, foul odor, fish gasping at surface, or nitrate above 50mg/L. If water is clear, odorless, and fish are active, no urgent change is needed even after 7 days.
There is no universal weekly water change rule. Your schedule depends on fish load, plants, and filtration. Planted tanks may need changes every 15-20 days; bare tanks with large fish need weekly changes.