I've never heard of any side effects from too much biotin. It's a water soluble B-vitamin, any excess is just excreted in the urine.
Living in Oregon, I can also attest to the fact that hooves will chip even when it's been raining nearly non-stop for 6 months. Did you switch farriers when you switched barns? I've noticed that some farriers' trims just seem to chip more, and even with the same farrier it might chip more or less from trim to trim. If you're really seeing a lot of chipping, I'd re-evaluate if the farrier is doing a good job or if you're going too long between trims.
It wasn't clear to me from your original post... When you moved barns, did you go from hay + Healthy Edge to pasture + hoof supplement? Or is he still getting Healthy Edge?