From my experience, I started off with a two headed frogspawn to having it split into 23 and also break off on its own having frogspawn's in every corner of my tank...
I just sold the thing yesterday for 80.00.
It just splits on its own, never bother a frogspawn when it comes to splitting because you will mess with its natural 'circle' polyp extension growth. Get what I mean? Just let it take its course, its bone is very thick compared to most corals.
I never fed mine, my clowns just used it as a host.
And for the corraline issue, I don't know because I can't see your whole tank. Glass encrusts faster with corraline than rock. But me personally, your frogspawn looks good its just a night time shot so its closed. Put up an open shot with daylight fixtures turned on and then we might be able to diagnose an issue, but I highly doubt it since frogspawns are very hardy corals.
And remember, do not try to split it faster, it does it when it is ready!