We found that students should be involved in bringing in the aquarium cobbles. An obvious source for cobbles is a nearby stream. Students should be asked to bring stones of over a 1" diameter. Tell them to look for golf ball size, though the stones needn't be round. All stones brought into the classroom for the aquarium should be cleaned with a stiff brush, cleaned again with a brush soaked in chlorinated water, then rinsed thoroughly and allowed to dry for at least 72 hours before being placed in the aquarium.