Exactly how much weight can a 30g breeder hold? I have a very good lfs, and I asked them about how deep the sand needs to be for Julies. They said about 3-4 inches deep. According to an online calculator that I found, I'd need a bit over 100lbs of sand to get the desired depth, and then add the rock to that... Will the Julies dig around in the sand enough to keep it from building deadly gasses? Or will I have to sift the sand during a water change?