I will be setting up a mbuna tank very soon and only have a couple pieces of ocean rock which I want to change, what sort or rock am I looking for, what shops can I get it from an the general price I will be looking at
You have wider scope with a Mbuna tank, as they like harder water you can go with both the limestones and slate/granite types.
Basically avoid things with lots of odd colouration or veining that may be heavy metals that may leech (there are veined rocks that you can buy that are safe if you know what you're buying) and you're generally good to go for hard water tanks.