Not really sure why you just NOW be seeing brown algae this late into the set up. Ottos love to eat diatoms, but other than being a little annoying to look at, brown algae doesn't do much in the way of harming plants. Usually, it just goes away as the tank finishes cycling. That's usually when you start seeing other algae problems take over (thread and dust algae).
That's a really, really colorful 20gallon you got there Fisherman. Well done!! Just stay patient with it!