sweety

Sorry I can't really give you any advice as i'm new to the hobby, but I also keep Tropical fish & Koi. With fish keeping you have to be carefully of the PH & water hardness for your fish among other things & crushed coral is often used to increase the waters PH & hardness. I would think the calcium in the coral would leak out into the soil & increase the soils ph up to about 8 & poss increase the hardness of the water in the soil. I would think if the tree you were thinking of planting liked acid or neutral conditions then it would slowly die due to the conditions the coral would poss cause.

I'm sure someone will be able to give you a much better answer than I have