The brown algae could be diatoms. Which is common in new tanks -you should see how awful my 38 looked during its first month set up. Helps to keep manually removing it and doing water changes. Or get some algae eaters- otos really like that stuff but the also do better in established tanks so it's a tossup. Coral will make you water harder- hopefully your water source is not already high ph.
Are you feeding the plants? I don't see any mention of fertilizers...
Hopefully someone else will chime in here, I'm not an expert!
10 gal planted- male plakat betta, two nerite snails, malaysian trumpet snails | 38 gal planted- cherry barbs, kuhli loaches, oto catfish, nerites, mts