I know the tags are the things in the original post that are the main ideas, like fish, plants, planted, light, food, etc. So if you start a thread about a South american tank, than some tags might be fish, south american, cichlid, plant, etc. But if you don't say "cichlid" or "plant" in the original post they will not be tags. Try just making a thread with a pretty short title, using the same example, something like this "55g south american tank". Then don't put much info in the original post, and make a follow up post in that thread with more info. It might work.