Hi Rod. Just wondering what your reasoning is behind considering this hive tainted after requeening and several brood cycles. Couldn’t it even be they bred up some resistance and you could be throwing out the baby with the bathwater? Sure you know what you are doing, the question just keeps bugging me.
I just realized that I didn’t address this part of your question directly.
What I actually meant was that you take the 5 most full (brood and food) frames from the weak hive, and put them into a 5 frame nucleus box. If there are undrawn or empty frames, leave those out. Once the colony has recovered and is filling the space with plenty of bees, you can expand back into an 8 or 10-frame box.
Chalk brood can occur during warm dry conditions too like happened to me in summer.
The warmest and driest period of the year precipitated an outbreak. Certainly I had an underpopulation issue and when I happened to find Michael Bush’s advice (as per his link above) it really helped control it.
The Australian Beekeeping Guide by Goodman and Kaczynski (page 92), suggest, (following them noting that it can occur in warm dry periods), that, “poor conditions such as limited supplies of nectar and pollen may be a factor. Moving hives to good conditions or feeding colonies sugar syrup and protein supplements may help recovery. While high protein pollen is preferred, any pollen is better than none at all. Ideally the bees should have access to pollen from several plant species for a balanced nutritional diet.”
Chalkbrood spores are viable for decades, even after a few brood cycles I don’t think you could ever say your hive is cured unless the bees leave and you have it irradiated.