typically people point their flow towards the other side of the tank - coralaine needs good flow to grow fast - point some of the circulation towards the rock and you'll see a difference.
i have kaelini rock, real big rock i had o break it down. i got 100lbs. for 300 bucks. there is a guy that lives here in jersey that sell all kind of LR out of his house, his name is bernie you could contact him at seatrademarine.com if you are looking for LR. he is in south jersey but you do not have to pay shipping