Sign 1. Pond waste
Leaves and windblown debris sink to the bottom. Without a skimmer this debris releases gases that grow harmful bacteria and unbalance the water.
Sign 2. A smelly pond
A rotten-egg or dirty-sock smell means parts of the pond have turned anaerobic and unbalanced. It comes from the waste above releasing gas.
Sign 3. Wrong-size filtration
A pump that is too small is a very common cause of problems. Match the filtration to the pond volume from the start and do it right the first time.
Sign 4. Algae outbreaks
Causes include too many fish, heavy rain, overfeeding, poor circulation, or the pump being off. The biggest cause is not having the right ecosystem, so make sure you have enough of the right plants.
Sign 5. Cloudy water
When you cannot see your fish it is time to clean. Caused by overfeeding, an algae break-out, or the wrong filtration.
Sign 6. Floating scum or foam
Usually overfeeding. Uneaten food sits and breaks down. Feed your fish properly.
Sign 7. Unhealthy fish
Fish gulping at the surface or dying off signals low oxygen, too much muck, or trouble at the bottom. It can harm the whole pond, plants included.
Sign 8. Green water
Single-celled algae turn the water to pea soup. Harmless to fish but unsightly. Removing and preventing it is part of natural maintenance.
Sign 9. Brown and lifeless
Weather-related brown clears in a few days. Persistent brown comes from high fish numbers stirring the bottom or soil eroding from the banks.
Sign 10. Tea-coloured water
Tannins from plant matter breaking down give the water a tea-coloured, bitter look.
Quick answers
A short recap of the most common questions readers send in after spotting one of the signs above.
Things are out of balance. Anaerobic pockets are releasing gas, usually from waste sitting on the bottom.
Check you have the right size pump for the pond volume. Undersized filtration is one of the most common causes of trouble.
Clear it. Net, skim or vacuum the debris off the bottom before it breaks down further.
Correct the plant balance first. The right plants in the right quantities do the work chemicals can only mask.
Do not overfeed. If food is still sitting after a few minutes, you have given too much.
Stop feeding. Uneaten food is the usual culprit and the pond needs a chance to clear.
Gulping or dead fish can mean waste is removing oxygen from the water. Treat it as urgent.
Fancy tackling it yourself?
If you are taking it on, this is the kit you will want lined up before you start.