Ken:
There's many possibilities to consider:
First, I've also heard that the electrolyte lasts indefinitely, but the brightener does not. It gets consumed during plating, so you have to replenish it every so often, whenever the parts start to come out dull again. Until now, I've never heard that you can add TOO much brightener, so I can't help you there.
I used the recommended 1 teaspoon per gallon to begin with, and when I notice parts not plating as bright, I just add another half teaspoon. So I guess I've never over-brightened.
How many quarts/gallons of electrolyte do you have and how much total brightener have you added?
You say you've got a bolt that's .5 sq-in. That must be a tiny bolt. Surface area of bolts can be quite deceptive. My initial "guesses" turned out to be way less than the actual calculated surface area.
For instance, a 1/4" bolt, 3/4" long, has 1.75" surface area. My initial "eyeball" estimate was no more than 1", so I was way off.
If you're getting lots of "frothing" from something that small, then that's WAY too much current. Even something as small as 2 sq-in will only give off light fizzing.
Another possibility here is that you don't have good electrical contact with the bolt. If the connection isn't good, then most of your current is going into plating the hanging wire, and not the part. How have you got it wired? Is your connecting wire in the electrolyte? How did the wire plate?
It's possible that your electrolyte has been contaminated with someting else too. Anything unusual happen to it in the past?
Anodes shouldn't "go bad", but they do get consumed over time. As you plate more over time, the anodes will get progressively thinner, and ragged around the edges, as the zinc molecules are pulled off. They'll eventually disappear if you let them. I never do anything with my anodes except rinse them off in fresh water after a plating run. I've even let them sit in the electrolyte for 3-4 days, and they still plate fine.
I did a bunch of tests early on, using different current densities, with and w/out brightener, to see what worked best. We were discussing it on another thread too, and the links are here:
http://forum.caswellplating.com/electroplating-questions/4770-copy-cad-zinc-trouble.html#post24467
Do your results look anything like mine?
Sean