Water Softener No Longer Removing Iron

My house is about 3.5 years old.  We originally had a very bad iron
staining problem (toliets, tub, etc.).  My builder installed a
Northstar water softener a few months later.  This unit worked great
(no more stains) up until recently.  We have been noticing iron stains
on the toliets, and in particular in our large whirlpool tub.  The
water in the tub looks dirty and when the jets are turned on they
produce "iron bubles".  The water looks clean coming out of the
faucet.

I took the softener apart and removed all of the salt.  A large (1.5
ft. high) mass of salt was found at the bottom.  The water was over
three feet high in the tank.  After cleaning the unit and replacing
the salt I ran some Sears water softener cleaner through the brine
well.  Now the water (and salt) are about 1/3 of the way up the tank. 
Everything seems to be working fine.  However I'm still getting iron
in the tub.  Could the Resin be fouled?  (it was a red colored, but
I'm not sure this isn't normal).  Any ideas why the softener would
work for three years and now all of the sudden stop working?  I ran it
those three years without ever running any cleaner through it.  Should
I be using something other than a softener to remove the iron?

Any suggestion are greatly appreciated.