I have gravel in my tank now. I have a 10 gallon tank and it is currently going through the fish-in nitrogen cycle. I have 4 cory catfish and I don't want their barbels to get hurt when they try to get food. When the nitrogen cycle is done would it be safe to switch from gravel to sand or will all the beneficial bacteria be removed when I get rid of the gravel? If it would be removed, would it start the whole nitrogen cycle over again? If it is safe to switch over without screwing any thing up, what kind of sand would you recommend?