black gold vs diamond

I have fed diamond premium adult (green bag) for about 15 years. In those years I have tried many other feeds including blackgold. I have had to go back to the diamond to get a tight hard stool. I've been told to make a feed switch slow by mixing the feed before totally switching to a defferant feed. I've tried that and I've swiched suddenly and it still did'nt work. The only feed that I've fed other than diamond for any length of time and felt the dogs do good on it was evergreen performax but it's had to get here. Just my .02