Bottom gravel is clogged by sludge


My bottom gravel becomes dirty very quickly (probably due to fish waste and uneaten food), I then have to clean it after a certain time. What can I do against it, is there any treatment?

it is in this case advisable to simply use a gravel washer during the water changes. Generally, the problem occurs mainly with coarse gravel. The gaps are simply larger, allowing fish waste and uneaten food to sink in, while they stay on top in case of fine gravel and sand, where they can be washed into the filter more easily. Snails living on/in the gravel (especially Trumpet snails) are useful in this case, they loosen the bottom gravel and even take up fish waste for their nutrition.

It is important to differentiate between organic and inorganic sludge. Organic sludge appears slimy and is rich in organic nutrients such as protein and carbohydrate remainders. This sludge (typically fish waste and uneaten food not or not entirely broken down) leads to oxygen consumption and may affect water quality, it should therefore be removed. According care advice refers to this kind of sludge. 

Inorganic sludge, however, appears flake-like, it is settled by useful bacteria and actually is an effective biofilter. It is only optically annoying, if at all, and need not be removed from the aquarium.


Best regards

sera GmbH

Dr. Bodo Schnell


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