Water change rate and filter cleaning


I purchased an aquarium (60 cm x 30 cm x 30 cm) about 1 1/2 months ago and set it up with plants on sera floredepot and gravel according to the instructions from the pet store staff. I have added fish in the meantime. Considering aquarium maintenance, the lady in the pet store told me to alternately clean the filter media thoroughly every fortnight…

This is alright if it considers only the prefilter media, however it is necessary only when these are clogged so densely that the water flow rate goes down considerably. On the other hand, the biologically active main filter media should by all means be cleaned as rarely (!) as possible, as the valuable bacteria cultures will otherwise be destroyed every time. If the biological filter does not allow for at least 6 - 12 months without cleaning, it is overburdened or undersized (which actually means the same).

… or change about 1/3 of the aquarium water - this means to change the water only once per month. However, I have read in the very informative articles on the sera website that you should change the water once weekly. I am now somewhat uncertain. What is correct? You will probably say the information on the sera website is correct, but how do you explain it? I simply want the best for my fish. What advice would you give me?
It is basically correct that 'many roads lead to Rome', as the proverb says, and also aquariums with infrequent water changes may function well. Generally, I rather recommend more frequent water changes of about 20 - 30 % instead of rare, very large ones (sometimes you can find recommendations such as '70 % every 6 months, or similar): The variations in water composition are simply smaller. A sawtooth shaped graph will be the result if you plot the overall water qualiy vs. the time. In case of many smaller water changes, this graph has more but much smaller teeth, and smaller teeth in the graph means less change (linked with stress!) for the fish.

Best regards
sera GmbH

Dr. Bodo Schnell


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