Setting up a plant tank(90G)...

I was curious about using some rock that I've had for 10 years(in
cichlid tanks)...

Its cave rock. My LFS has highly recommended that I NOT use it in the
plant tank because the water would leach minerals and stuff out of it
and harden my already hard water. I used a large portion of RO water to
soften my water a bit and the LFS store guy added that it would increase
the leaching even more...

Anyone got any ideas? I'm looking at going with Lace rock if it turns
out that plants dont like this rock..