It was good reading about the proper sugar water proportion for 2:1 syrup. In the discussion it was mentioned that people add a bit of vinegar, leman juice, orange juice - anything acidic to the mix. Has anyone had good sucess with adding oxalic acid or ascorbic acid (vitamin C)?
How about adding other vitamin supplements?
Personally, I'd just go with the syrup and not add any other concoctions. As far as vinegar goes, one of my bee books says it isn't good for bees. On one of the Yahoo groups not too long ago there was a discussion about adding Vitamin C. Some of those guys might have more to say on it. This is a little off your topic, but still might be pertinent. It talks about diseases:
"One official report said diseased bees were short of nitrogen, because their distended rectums contained much pollen. This followed the mistaken belief that adult bees usually did not need protein food and, when they did, that pollen was unsuitable; so it was recommended that all pollen combs should be removed in autumn and the colonies fed beef extract to make good their supposed nitrogen deficiency. This would certainly kill or seriously cripple any colony because pollen is essential for adult bees and beef exract is poisonous for them mainly because of its salt content. The ruinous idea of removing so called "pollen-clogged" combs persisted, however, and was widely practised fro many years." Leslie Bailey: 'Honey Bee Pathology'
Considering that bees will drink from a swimming pool, and that the behavior likely get reinforced (ie the bees don't die and communicate the location ) you can likely add many things to water/syrup. But why?
I have heard that "stinky" stuff like vinegar makes syrup more attractive to bees. I also have heard that it helps retard the growth of foreign matter in the syrup. But you do not have to convince a bee hive to take up a gallon or more of this stuff when you put it right next to them. It gets put to use fast so they do not need anything extra.
I have added small amounts of things to my syrup without noticing detrement or benefit. Now I just do not worry and do not add anything other than elbow grease and sweat du brow.
Had a patient tell me that his son had "invented" strawberry flavored honey with other flavors on the way. He put out strawberry concentrates, the bees put it up for stores yielding the honey upon extraction. Not much of an idea and I would not eat the stuff...
I don't put anything in the syrup. But if the mold really bothers you (I assure you it does not bother the bees any) then something acidic can prevent it. Anything with smell in it seems to set off more robbing, which is a problem anyway when feeding. So I don't like to add anything.