I routinely have phosphates up at the .4 level and have very happy torches. I think consistency is most important with any coral. With a healthy frag, there should be no issues of bacterial infections. I think a lot of the infections come from premature fragging where people cut the flesh and are asking the coral to heal from a dirty blade cut. When I cut, I wait for separated flesh and don't seem to have those issues. (knock on wood) Feeding them likely helps a lot.