My purple LTA did that for a long time, I just kept water parametres normal, weekly WC of 25%, increased flow and tried feeding it daily real small bits of fish. It would only eat maybe 20 % of what I offered it but after a few months it came back, real slowly though! It was lookin real bad, not attaching to rocks and lookin real slack. Now its back to how it was but has green tips now :-?