You don't need to feed anything special, just watch your Cal/Phos ratio.  We've never had a problem if we keep it 1.2-1 or higher.  If you have high calcium levels in your water, you can also give that credit - we've gone down to 1:1 in the ration at yards with high calcium water without problems, even with high by product diets.
The bottom line always is, sample your feeds and balance your diet for all nutrients.