I've had the same problem when using a commercial grade borax. Switching to a borax grade made specifically for curing bait solved the problem. I think the grade or moisture content of the borax is the key, and this can be inconsistent when shops buy it bulk and fill there own plastic bags for sale. Pro-cure puts out a borax thats great. It costs a little more, but you know what you're getting and you know it won't burn your eggs.