u/bsjaidik

I do weekly water changes but recently my nitrate went up, and im getting concerned. My two ranchus seem fine but i noticed one of my ranchus wen is kind of injured and im not sure what to do (ill provide images below) should i quarantine my fish? and how can i get my nitrate levels to 0. Please no judgement here just someone who is trying to keep their fish healthy and safe

PS. brown algae has been growing inside my tank for about two weeks and ive been scrubbing it but it keeps re growing