Re: weak hive- what to do
Another option you might consider is...
Swap positions of the strongest hive with the weakest hive and requeen the weakest hive. The field bees the weaker hive gets from the swap will give it a boost of field force and requeening it will give you fresh genetics and replace the queen not performing so well. Over time the two hives will somewhat equalize in strength from the swap and requeen.
20+ years, raise my own queens, feed when needed. I treat, but have not perfected varroa management yet.