Coastal Pebbles.

I've got some nicely rounded pebbles from the coast can I use them in a tank or would it be ill advised?
They've obviously going to have salt mineral on them but would boiling them like bogwood get rid of the impurities?

Boiling rocks can be a bad idea. Some rocks have air pockets inside, but you can't tell which ones from the outside, and boiling can cause the air to expand which explodes the rock. Just pour boiling water over them.

Also, check the rocks for signs of metallic looking veins. These can leach metals into the water.





And boiling bogwood is not recommended either. It breaks down the fibres so the wood falls apart quicker. Again, pour boiling water over wood, don't simmer it in boiling water.