Water change

Changing the water is the most important maintenance in aquariums. Removes accumulated waste products and restores consumed trace elements.

Detailed explanation

The concept is trivial: you remove a part of the old water and replace it with new prepared water. The practice has its subtleties.

In marine aquariums the standard water change is 10-15% weekly. The new water must be prepared at least 24 hours first: RO water, dissolved sea salt, heated to aquarium temperature, aerated. Never pour salt directly into the aquarium. Never use freshly prepared water without checking salinity and temperature.

A trick that few people use: vacuum the bottom during the change. Organic debris accumulates in the substrate which decomposes, releasing phosphates and nitrates. A bottom siphon removes this debris as you change the water.

In planted freshwater aquariums, the water change has a double function: it removes excess nitrates but also takes away the microelements that the plants have consumed. The weekly 30% is the standard for a Dutch aquarium.

In ponds the water change is more complicated due to the volumes involved. A 5000 litres pond requires 500-750 litres for a change of 10-15%. A filling system with dechlorinated water is needed. Many use in-line activated carbon filters on the water barrel to remove chlorine on the fly.

In winter the changes in ponds are reduced because the fish are in torpor and produce little waste.

How it is measured

It is not a parameter. But the post-change parameters (nitrates, phosphates, salinity) confirm that the change was effective.

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