I think the concern is for the fish... but I like the rocks, I have some nice lace rock i've been scared to use. my water is soft and has low ph, so I worry the rocks would spike the tank.
Well I could check the hardness and pH--would need to purchase new test kits--but I have had these fish and others in our extremely hard tapwater and they all do just fine. For just keeping fish healthy I think that the important thing to have in mind is that conditions should not fluctuate drastically. Of course, breeding might be a different matter. Many fish do apparently require water chem params within a certain range for successful breeding.
My little Pilea nummularifolia plants are looking good. I have these stems planted on Nano Trellis Rafts.
This plant is really perfect for growing this way. It makes a nice and tidy foreground feature and it's an easy grower.