[header] How to empty an aquarium [title] Transfer the fish out of your tank. [step] You'll need to remove your fish and any other aquatic organisms before you can drain the water out of an aquarium. This requires great care, though, as fish tend to get frightened by this process and may become tangled in the nets. 
[substeps] Choose the correct net size so that your largest fish will fit inside. Even if the nets are large enough, you'll still need to exercise caution so the fish don't get injured during the transfer.