Nitrate it just one detectable nutrent.. rock can and will absorb right about anything nutrent wise (not to mention the nutrents that are naturaly in the materials used to make it if its DIY
rock) that would include PO4
ect. ect. ect... that was were I was going with that..
The rock itself will disolve in PH
less then 8.2 or so and will disolve untill the KH
brings the waters PH
up to that level.. soooo.. if the fish can aclimate to a moderatly high PH
then yes they should be fine with the rock... Curring the rock isnt going to change the propertys of the minerals contained in the rock and what levels of acidity will disolve them.. IMO