what can I use to water seal some slate rocks?

[Cohazard]

I've got some slate tiles that I want to use for my tank, but I'm nervous about some oxidized mineral deposits that look like rust I've found on some of the pieces.

My idea is to use some kind of water sealer, in several coats, to hopefully seal them from leaching anything harmful into the water.

Any ideas on what I could use that would be tank safe? Thanks.

 

[Dan F]

I wouldn't bother. A bit of iron in your tank won't hurt anything - I would be more worried about the sealant flaking off over time.