my coraline algae turning white

[tde123]

i am adding one capful of purpleup every day in a 55 gallon aquarium no corals 2 fish and a cleaner shrimp my calcium is at 450 and i am running T-5 lights does anyone have any idea what could cause this

[tashier]

What is your alkalinity and what tests are you using?

[hng]

Are your t5 lights new? My coraline bleached after I replaced my vho's with the more powerful t5's. Other causes: temp spike, low alk, low calcium