Drilling Rock?

As long as the rock won't change your water chemistry it should be fine.

 

Masonry and tile bits will work with some rock but fiji may not be worth it.

 

You can use many different rocks in a SW or reef aquarium as long as they do not release phosphates or heavy metals into the water. If you see any rust on the rock it is no good because it will release iron. Also if the rock has come from a polluted stream or any area where chemicals were used they can leach back into the system. Thats why many people dont use rock from their backyard in their tanks, although I have in FW tanks many times with success. Also do NOT use lavarock very porous but if Im not mistaken releases phosphates.

 

Whats the worry with iron. What else will it do but turn to rust (ferric oxide) and bind phosphate?

 

In smaller amounts it would be ok since most of it is bound in an oxide state which is inert at alkaline pH values. Too much could discolor the water though and there are exceptions such as fools gold which is iron pyrite which can
1. It has a strong acidifying effect, i.e. it drops the pH.
2. In addition to iron it sometimes contains small quantities of other more dangerous heavy metals such as lead, zinc, and copper.
3. Because it acidifies the water it can 'unlock' heavy metals into their toxic free-ionic forms.
I come from a FW backround so maybe this isnt all true for SW, but I dont want to risk a system worth thousands of dollars so I can have a rock I liked in a stream