Troubleshooting
Fixing common pond problems, from green water and string algae to cloudy water, low water levels and stressed fish.
Algae & green water
Fixing common pond problems
Most pond problems have a handful of causes: too many nutrients, too little filtration or oxygen, too much sun or a small leak. Finding the cause, rather than just treating the symptom, is what stops problems from coming back.
Algae is the most common complaint. Our guide to pond algae explains the difference between green water and string algae, quick fixes, and how to keep algae away for good. For persistent green water, a UV clarifier is often the most effective fix.
Many problems trace back to equipment. A clogged or undersized filter or a pump that's lost flow can turn clear water murky within days. Check your setup against our guides to pond filters and pond pumps.
Fish problems are usually water-quality problems. Testing for ammonia, nitrite and pH tells you what's wrong; see our fish pond guide for safe levels, and pond fish in winter for what's normal in cold weather.
Prevention is easier than cure. Regular, seasonal care from our pond maintenance guide prevents most of the problems on this page.
Common questions
Green water is caused by tiny floating algae fed by sunlight and excess nutrients, often from too many fish, overfeeding or decaying leaves. More shade from plants, better filtration, a UV clarifier and feeding less usually clear it within a few weeks.
Ponds lose some water to evaporation, especially in hot, windy weather and with waterfalls or fountains. If the level drops more than an inch or two a week, check for a leak around the edges, the waterfall or stream, and plumbing connections before suspecting the liner.
Fish gasping at the surface usually means low oxygen or poor water quality, common on hot nights or after algae dies off. Add aeration or turn on a fountain right away, test the water for ammonia and nitrite, do a partial water change and stop feeding until levels improve.