Here is your guide for good and bad foods in terms of phosphorous:
http://thesquirrelboard.com/forums/s...sphorus-Ratios
You're looking for a ratio of 2:1, calcium to phosphorous. Corn varies, but if memory serves, it's something like 2:80, so quite horrible. The docs above will show you.
I would suggest that for the time being, because he's had a relatively poor diet up until now, that you seriously restrict his phosphorous intake and give him extra calcium. The cuttle bones and antlers that I recommended earlier are good at both keeping the teeth filed down and supplementing calcium. I would also recommend getting the calcium powder from Henry's while you're ordering blocks. You can sprinkle it on his other food for awhile to try to get him back up to par. Do you know what metabolic bone disease (MBD) is? We see it all the time here. It results from a low calcium diet. All the calcium is leached out of their bones over time, and then when they basically have none left, they start showing signs such as lethargy, paralysis, and seizures. Death follows shortly if it's not caught in time and treated immediately. Your guy could have weak bones at this point.
http://www.henryspets.com/calcium-carbonate-powder/
Also, you said that he can't crack nuts? Have you checked his teeth to make sure they're not over gown? They grow something like six inches a year, and if not kept worn down, they can kill them.