I am thinking of using sand as a substrate for my new 75 gal. tank. I have read MANY of the threads in this site and have learned a lot but I am still left with a few questions. 1. Which sand would have the biggest particles and still be considered 'sandy' enough for Corys? 2. I prefer darker sand or mixed color. I read that play sand has more silicates than other sands and could cause problems with diatoms. Is this really true? 3. I also read that 'Black Diamond' sand can be rough and sharp. Will it damage the barbels on the Corys? 4. Are there different particle sizes for pool sand or does it just come in fine? 5. Is aquarium grade sand the better way to go even though it is much more expensive? 6. What is the easiest way to prep/clean the sand before use? Sorry I have so many questions. Any advice/opinions would be greatly appreciated.