I just finished planting a 75g tank a little over 3 weeks ago and am
wondering how to tell when plants have used up all the nutrients in
the water. The tank has basically already cycled do to pre-existing
bacteria from the filter. I have new growth on the plants but am
noticing a kind of brown algae forming on the leaves of some. I know
brown algae is common in a new tank but was wondering how I could get
the plants to out compete it. Currently houses 2 otos, 3 SAE, 1
rubber pleco, and 12 amono shrimp and 5 rainbows. 7-10 days in
between water changes, pH ~7.2. 210w of compact lighting on for about
11 hrs a day. Pressurized CO2 injected as well. Onyx/flourite mix
substrate.

When should I start fertilizing? Should I instead look into
purchasing more oto's as I know they relish brown algae? Also am
getting green spotted algae on the glass or should I adjust something
for now and fertilize a little later. Its a beautiful tank now and
would really like to keep it this way.

thanks