">Is there a problem with mold or yeast activity if the
syrup remains in the feeder too long?"<
 
Yes, there is certainly a problem with mold...I do not know about yeast.  I
suspect it is highly temperature dependent.
 
For this reason, if I am feeding a weak hive or nuc, I start out with only
1-2 gallons in the feeder as want to see it entirely consumed within 2
weeks.  I have been told that 1 teaspoon of Clorox or 1 tablespoon of
vinegar to 5 gallons of syrup will not hurt bees and will prevent mold.
This is interesting as the Clorox would make the syrup more alkaline and the
vinegar would make it more acid.  Yet both are claimed to work.  Because of
the seeming contradiction between alkaline and acid (in general, mold would
rather grow in alkaline solution than in acid) I have always been afraid to
try either.
 
Lloyd
[log in to unmask]
Owner, Ross Rounds(tm)  the finest in comb honey production.