How about just putting all of it in a big ol' bucket and then you won't have to wonder if this one or that one is fermenting or not...the whole thing will be fermenting at once and you can clearly see and smell the signs of fermentation and you can just feed out of it until it's almost gone, add more feed and water, stir it, start feeding out of it the next day and the next and the next until it gets low again.... and repeat the cycle over and over ad infinitum.
Gnats are usually attracted to anything rotting or fermenting, so I'd say the one attracting the most gnats is the one with the highest level of fermentation going on.
Curious...why would you use a complicated and fussy system of jars and a daily job of messing around with dumping, refreshing, etc? It really is much more simple than that and can really streamline your chores if you just feed out of a bucket and be done with it...unless, of course, you like fussing about with small containers and such, then I'd say "Carry on!"
...