what did you use for cook it with? if charcoal then just 1 layer on top would be fine with your rock about 1 - 1 1/2 inches deep. If I add just a little too much I will blow up my load also, have done it plenty, also mixing high grade pinhead coral or the dark glassy stuff in with some of the toughe polyped will blow it up also, those darker glassier pieces need to go underneath, got any pics of the before during and after?