my turn.. sps crash..

[Maverick00]

Ive been on vacation for the last 3 weeks and got my roomate to look after and dose the tank. however weeks BEFORE i left i noticed some problems with a couple pieces of sps bleaching and RTN'n. I got back yesterday to find the RTN is very slowly progressing on all my sps. Birdsnest and acro pieces are the main corals affected. (the rest of my zoas have also shriveled up and died) All lps is fine and opening. There are a few things i have changed in the last couple of months. Bulb changes (one bulb at a time) from 4 blue plus, to 3 white and 1 blue. Im not sure if that could have been a possible cause. I also started using an RODI unit as well as switching from biopellets to phosban. Any ideas on trying to narrow this issue down? Im going to try to frag the remaining pieces. Frustrating... Ill try to get some pics and water paras later today. Thanks for any help