Phosphate test

I started getting some green algae on my glass so I thought I would get a phosphate test kit... It's a little confusing my level is showing 0.5 on the test card but the numbers about I've looked up online are showing a stand 0.03.. Does that mean my phosphates are a little high? Extra zero was throwing me off so I'm a little confused i'm assuming that it's a little hike but I don't want to read it wrong... Should I treat my water at this point? I do have Phosguard.. Should I use it?