This is a discussion on indentiying fish within the Freshwater and Tropical Fish forums, part of the Freshwater Fish and Aquariums category; -->
Sand would be best. My black kuhlis love to dig through it looking for little bits of food to eat, and it won't wear ...
You can buy sand from a fish store, but a much cheaper way is to get a bag of play sand from a store like Lowes or Home Depot. They sell 50 lb bags for less than $5. You have to rinse it really, really well before you can put it in your tank without it clouding up the water, but I think it's worth it.
Also keep in mind that with sand, you'll need to keep it stirred so that it doesn't form dead spots. You can stir it manually with a plastic fork or something when you do your water changes. Your loaches will help you keep it stirred some, as well. You can also get some Malaysian trumpet snails which will burrow through the sand and stir it for you.
also could i do half tank sand and half gravel? my snails i got like the gravel and it hides there babys well not that i care cuz i started with one and now have more then 14 but i put some in my cichlid tank as well and my fish store dose buy them back after they get so big[/list]
For a saltwater tank it's really best to use live sand or aragonite sand from a fish store. Usually play sand is just a regular natural sand color. I haven't seen different colors of it, but I would be inclined to avoid any colors other than natural.