staghorn algae I know that all too well ! It didn't come in with any plant, so you can relax ; it's a deprivation algae ; in my case appeared when I had too much light , too soon ; you're day 32, are you sure you don't have too much light ? I see you have led, you should turn them on 8 hours a day, but less than 50 lumen / liter; on the other hand your CO2 diffuser is way too close to the surface, your wasting CO2 ! even if your drop checker is almost yellow ! as a matter of fact I think you should lower your drop checker to see if it's the same color at substrate level