Most aquariums have rocks in them. Do take care, however, because not all rocks are suitable. The wisest option is to buy your rocks frogman aquarium shop, but this can be expensive if you need a fair amount to create the right sort of underwater scene. Finding your own rock for the aquarium is more fun, plus the fact that it's nice to get something for nothing. As a general guide, if you come across rocks that have thin lines or veins of metal in them, leave them alone. Test any other rocks that you collect with a few drops of vinegar. If the vinegar fizzes vigorously then these rocks contain calcium compounds that will make the water harder and more alkaline and are suitable only for certain fishes. Do not worry too much if a few lines of little bubbles come up,as most rocks have some small calcium deposits. Soak rocks that have passed the acid test for a week in a bucket of water to remove the acid and leach out any other impurities. In fact, it is a good idea to thoroughly rinse rocks that you buy from your aquarium dealer.
Before placing rocks in the aquarium, slope the gravel from front to the back so that it is twice as deep at the hack than at the front. This not only allows any debris to accumulate at the front, where it is easy to remove, but also provides a firmer foundation for embedding rocks.
