White/Lavender spots on glass?

[sweetxoxo31]

Hi All..
I have these hard, lavender'ish white spots on my back of my tank & glass...they are really difficult to get off unless you scrape them with your nail pretty hard...what are these and any tips on how to get them off???

 

[freeborder_01]

coraline algae. its the purple that grows on your rocks also. If you have a glass tank i heard a credit card works, i use razor blades but they rust after one use heh

 

[subielover]

Yup, credit cards get what my magfloat does not