Pink algae

New here and am looking for any reason for pink algae. I have a 22,500 inground pool and use Baquacil instead of chlorine, more expensive I know, but enjoy the positives from it. In the past two or three weeks, I have developed pink algae. Treated it yesterday with extra strength algicide and two pounds of non chlorine shock. I keep brushing it daily. What might be causing the growth of this pink algae? Thanks in advance