I would not kalk live rock, gobies and zoos. I never do that in my nanos anyway. Just change some water every week or so. No additives at all except maybe a drop of vitamins or something, so long as you use an established salt mix like IO as opposed to one of the new fad craze salts. Kalk topping in a nano is going to get the buffer system way off. Its too easy just to change some water. And a large piece of LR in a nano? Lots of room for decay inside that thing and that can change things for worse over night. It will be alright after it gets all the junk purged from inside it, but, any odd thing could die in a large rock and totally mess with a nano sized tank. That would cause low O2 retention for sure.