Some types of dry rock does leach PO4
Iv'e found the tonga branch is one of those that being said iv'e found the its best to soak any new dry rock in a pail of fresh RO
water test the water every 3-5 days you'll know if it's gonna leach if it does i change the water every 5 days until it test 0 then you can add live rock to seed just be sure to feed the new rock it needs an ammonia source.
Most people create their own problems by not following the basics and refusing to stock appropriate to their system. Gregcoyote 2013
SPS = Stability Promotes Success