My 10 gallon planters aquarium has been smelling well..like a fish tank. That earthy, swampy smell. About 2 weeks after reaquascaping my tank, I began to notice a strange odor when I would walk in the room. The problem is, its a guest room. There are a couple possibilities: it could be the horn wood rotting in the tank, or the detritus built up deep under the substrate. Is there anything I could do besides water changes to fix the smell?