I don't see any problem with adding more. I would only add a little at a time if possible. Turn all pumps off when putting the sand in and let it settle some before turning the pumps back on. I would rinse, unless live sand(then just drain), put it in a bowl or big cup, then try to lower the cup or bowl in the water without the sand going all over the place, when you get near or at the bottom, pour the sand where you want it(does this make any sense), some will get stirred up, but if you keep the pumps off for a little while it should clear up in no time. Good luck, you may want to feed before having you hands and arms in the tank, I don't know, never had sharks or eels, don't know how aggressive they are about you being in their space. I hope you stay here, sorry about you "clickish" feeling, I don't think it is bad here at all, some places are definitely that way.
I try not to be that way, usually just look for coral questions or equipment type help. Good luck and have a happy new year.
Matt