What kind of substrate should be used in a saltwater tank? I have heard that sandbox sand that can be bought from hardware stores is okay.

Sorry to say, but you have heard wrong. One more example of all the horrible aquarium information available on the Internet. A good book should always be your primary source of information. Top • I am setting up a fresh water tank 60 Gals with Flora Base for plants and will be adding Bala Sharks, Cat Fish, turtles, cray fish and tree frogs. Will the Flora Base harm the fish? Flora Base (by Red Sea) is designed for aquaria and will not harm fish at all. However, we do see some big problems with your plan. The Bala Sharks and Turtles will eat your plants. The Turtles will eat your Crayfish. Tree Frogs are terrestrial animals and cannot be kept in an aquarium. If you are planning on setting up a vivarium, with a half land, half water tank, please be aware that Bala Sharks will not do well in this situation. Top • I have a 55gal saltwater show tank. I want to convert it to a reef. I have a wet/dry filter.  more