Any honey varietals that are particularly bad w pH drops?
As a general rule, I think lighter honeys have more pH drops. I find it happens quite frequently with FL OB, and Tupelo.
Are there any steps that can be taken to reduce the likelihood of a Ph drop in a traditional mead during the initial fermentation?
There are several things you can do. Generally I check the pH during the first 24-48 hours of active fermentation as that is when the problem is most common and if I see the pH less than where I want it, I will use carbonates.
Potassium bicarbonate is usually easy to find in homebrew stores (or online). The potassium is taken up by the yeast to help them cope with low pH and the bicarbonate raise the pH. I add just enough to get the pH to a reasonable level - I don't try to raise the pH up to 3.8. The lower the final pH, the less like spoilage organisms can survive so I like to raise the pH the minimum amount necessary to insure proper fermentation and you'll almost never find me raising it above 3.4.
If you don't have potassium bicarbonate, potassium carbonate works just as well. Calcium carbonate will also work, but it doesn't give the yeast the extra potassium they need, and it takes longer to dissolve into solution so you have to wait hours for it to equilibrate so that you don't overshoot your target.
There are other things that can be used such as potassium hydroxide, but these things can be more dangerous to work with.
Now it is worth noting that if you use nutrients with a lot of autolyzed yeast such as Fermaid K or Fermaid O, these nutrients tend to raise pH. If you use the majority if your nutrients in this fashion, it may reduce the risk of pH drops. Roger Morse was a proponent of adding cream of tartar (4 g/gal) which can also provide effective buffering for a batch, though it will also add some acid flavor (which may be desirable).
I hope that helps.
Medsen