Why not foundationless?
That would be the best course, foundationless, but I do not know any beekeepers in Europe that go foundationless and do not need to treat.
We have to go step by step
100 years on large cells is a lot of time and we first have to teach our bees, what they have forgotten, in order to bee able to defend themselves successfully. And for this we need the 4.9 mm cell at the beginning, what apparently is the measure under which they come into harmony with nature. Just imagine that the smaller bees can fly into smaller flowers, thus also the compilations of propolis, polen and nectar are different. The propolis is the medicine in the hive and when the composition is natural, of course, the effect is much better. So first we have to get our bees used to build again samll cells, that takes several years and then we can release them and so they can build as they wish. There are some in our group that do this, but you have to start in the beginning, not in the end. (Photo D. Murrell v)
I think Michael Bush is the one who has the most experience in this way.
This is how the bees build, if they know how to do it and then they need not to be treated anymore.
As I said, I know nobody in Europe who works foundationless and does not have to treat. Also there are some who work with small cells, but omit essentials and therefore must treat.
The acids are actually just as bad for the bees as the other chemicals - they burn holes in the exoskeleton of bees, which are then naturally prone to disease. Erik from Sweden said, that the bees there, when the varroa arrived, resisted up to 20.000 mites per hive without showing DWV virus infection (deformed wing virus). Then they began to be treated with acids, and the consequence was, that they weakened the bees so much, that already with 1000 or 2000 mites appeared the DWV virus.
The interesting thing now is, that in Spain the resistance to the DWV virus is increasing (according to Dr. Fernando Calatayud, a biologist, Valencia, Spain). They do not treat there with organic acids against Varroa mites, but in Sweden they are used exclusively. This means that very likely the use of acids in the hives reduces the resistance against the DWV virus. This seems logical when one considers that these burn holes in the exoskeleton of the bee.
So we see that all this has a lot to do with stress and the immune system of the bees is enormously weakend.