Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
The brown algae is highly likely Diatoms. These things need silica to live, and sand and new glass are great sources. Clean it away, and remove it from the tank. If you get fish to eat it, vacuum their poop. If the silica stays in the tank it is recycled into more Diatoms.
I have not found that Opaline Gouramis eat it. Only get these fish if you are sure you want them. They are very territorial, and aggressive to each other (only keep one per tank) and sometimes to other fish.
Better fish to eat Diatoms: Bristlenose Plecos, Otocinclus.
Root tablets may work well for the plants you list. They have strong root systems, and are able to get what they need from the substrate.