is it ok to use rocks that you find outside. do you have to boil them, or should you not use them at all

well you should clean them off well (like boiling is a good idea), but you also need to make sure it doesn't change the PH of your water. You can take it and put it in a bucket of water. test the water before the rock and a while (few days?) after the rock is put in. Some rocks move the PH up or down, which is probably bad.

<_< i think, but im not sure that if you put vinegar on them and they fizz,you dont use them. for soft and medium/hard the safe ones are basalt,granite,quartz,slate,and hard sandstone. unsafe ones are soluble rocks,calcareous rocks, shells. and if your water is hard, safe ones are soluble rocks,calcareous rocks without metallic-ore veins. unsafe are rocks with metallic-ore veins.
sorry but i cheated on that i got the list from a book

Theres a post in the Goldfish tank section that covers the kinds of rocks you can use. Check it out hun