Water Garden Problems and Remedies: Acid, Alkaline, Green, Smelly Water and Leaks

Acid Water

When fish are prone to disease, sudden death, and red fins, water has high acidity (low pH). Other signs: oxygenating plants don't multiply well, biological filters malfunction, water snails develop thin, pitted shells.

Remedy: See 'Alkaline Water' below.

Alkaline Water

When fish suffer fungal diseases and gill disorders, water has high alkalinity (high pH). Other signs: oxygenating plants covered in slimy coating, water plants yellow leaves during full growth, water smells slightly of ammonia.

Remedy: Whether acidic or alkaline, the correction process is the same. To reach desired pH 7-7.5, start by changing ~25% of pond water. Then increase aeration—run a fountain/waterfall, turn on a filter or venturi aeration device.

Green Water

Caused by vast numbers of microscopic algae—not harmful to fish or plants but unsightly. In new ponds this clears naturally. If not, install a filter with UV clarifier, then when water clears by half or more, add more oxygenating plants to approach the desirable plant-to-fish balance.

Smelly Water

A balanced pond with fish, plants, and fountain/cascade has enough activity to prevent gas buildup. Faint odor: reduce water level by half, use pond vacuum to suck silt/detritus from bottom, top up with clean water. Acute problem: likely caused by oxygen lack in sediment, promoting bacteria producing methane and hydrogen sulphide (rotten egg smell). Drain pond (net fish first), extract silt, refill with clean water. Installing UV clarifier filter helps prevent recurrence.

Leaking Concrete Pond

To trace leak: turn off pumps/filters, let water drop to escape level. Leak may be in rendering—caused by excessive sun exposure or wear—or in base concrete from outside influences like plant roots. Small leak: repair with rendering application. Serious leak: install butyl liner as membrane to maintain water. If roots caused it, treat them before liner installation or they'll regrow and damage the liner, restarting the leak.

Pond Icing Over

Ice prevents oxygen entering and harmful gases escaping. Snow on ice blocks light for fish. Melt a hole with a saucepan of boiling water, or prevent ice forming with an electric pool heater. Alternatively, run a fountain/waterfall permanently—moving water never still enough for ice to form.