How can I lessen the smell of my aquarium? I have 3 kois in it. Any suggestions?

Answers:
Change one third of the water every week and put new activated carbon in the filter every two weeks. That will take care of the smell.

Adding chemicals is never a good idea. It just starts you down a slippery slope to too many variables.

Water changes and fresh carbon are the way to go. You should also be siphoning the gravel every two weeks.

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I would suggest adding an ammonia detoxifier because ammonia sometimes really stinks. If that doesn't improve the smell, replace your filter and see what happens then.

~ZTM