tank set-up

Question
I have a 55 gallon freshwater tank with Dania Zebra's & tetra's.  I am conteplating building a flagstone structure for the fish to swim thru & hide.  I'd like to know if I can put flagstone from the yard (I'd clean all dirt) straight into the tank or is there something I need to do beforehand to prepare the stone???

Answer
Rocks such as granite and slate are pond-safe as well as aquarium safe. Flagstone should also be safe as long as it doesn't bubble when in contact with vinegar. If it does then the stone contains calcium and is unsuitable for aquarium use. To test, pour some vinegar on the stone. Before placing the stones in your aquarium, immerse them in boiling water. This will clean them and  kill any unwanted bacteria that may be living on it. Hope all goes well.