Daytime, nighttime, moon cycles,...sometimes one cannot catch much of anything.
When I fish for them smelts, sometimes they will bite from about 3-5' below me to as deep at about 100' below me. When they are schooled very tight, they rarely bite. So when I'm marking like a big school that's packed and showing solid on my flasher for like a 10-40' band of smelt, I almost never get them to bite. When I can see individual smelts marks on my flasher, I do so much better. If the one at 20' mark isn't biting, I drop down to the one at 30', if not then the one at 40', etc.,..because one of them will more than likely bite.
Smelt biting and hooking up, is kind of two different things. To improve my hook up ratio. I do use a braid line between my weight and hook. About half the smelt I hook up with, are not hooked well. They fall off as soon as I get them out of the ice hole. So basically it's like the hook bend is just hooked onto their teeth and I reel in fast so they can't spit it out.