Okay thanks. I was just thinking about chaning 5 gallons of water every two weeks, and not use a protein skimmer yet. I haven't got a test kit yet. My LFS Store is testing my water every week right now. I was going to get a test kit maybe next week. (The test strips). All my levels were perfect so far. I think it might be the sand because one part of my floor in the aquarium is missing a section of sand, either of the water pump (circulation), or of one of my crabs/snails.
Thanks