I agree with RO water being part if not all of the problem. It doesn't have the minerals that ground water has. Also a lot of organic ferts don't have the trace elements that chemical ferts have. I use tap water and rotate ferts. I use Bio-Gold, seaweed/fish emulsion, and 7-9-5 Dyna Grow along with MirAcid for those trees that like it. I believe that different ferts offer different things to the tree and personally I would never apply any one single fert year round. That's just my humble opinion. BTW what Bay Area are you in? If you're interested there is an excellent BC collector/grower in La. named Guy Guidry here's a link to his site
http://www.bonsainorthshore.com/ if you've never been there check out the Twister.