I'm not the expert, I'm just getting mine cycled. But I would rather it be right from the start. If it were me I would scoop out as much of the crushed coral as possible and replace it with live sand. You have roughly a 40 gallon tank, so I would say about 35-40 lbs of live sand would do you good.
I would also consider ditching the canister filter and going with a sump. I started out with a 60 gal
. aquarium with a canister filter. Then changed my mind and took down the 60 and returned it to the store (because I couldn't fit a sump in the stand) and started over with a 75 gallon and built my own stand. Just my opinion. But I think the crushed coral combined with the canister filter will mean uncontrollable nitrates.