I have a 20 gallon tank and haven't owned fish before, but I understand ammonia (and eventually nitrates) can be problematic.
Partial water changes are what we typically do to reduce nitrates, and the biological filter will eventually remove the ammonia, once it has become established. Add fish slowly and do not overfeed to avoid ammonia issues.
That being said, if you have really large fish or goldfish, White Diamond is a good idea. You add it to a media container for the Penguin filter (media container is sold separately) or you can add it to the toe of a nylon stocking and place it in front of the cartridge.
Date published: 2017-11-22