Byron said:That brownish (rusty brown) algae seems to be diatoms, if you can easily rub it off with your fingers. If you cannot, then it is one form of brush algae. From the photos I am suspecting diatoms.
To the cure. Diatoms are most often associated with new set-ups, during the first 2-3 months. After this it should not return. If it does in an established tank, we need to look at light intensity, plant fertilizers, and possible silicates in the source (tap or well) water.
If it is brush algae, it is caused by an imbalance between light (intensity and/or duration) and nutrients. Restoring the balance will deal with it.
Byron.
Zikofski said:ottos do love diatoms and so do shrimp, cherry shrimp and amano shrimp are good, i believe cherry's in large numbers are better than amano's, but yea diatoms are a pain i went through that stage in one of my tanks and its cleared up now but still going through the diatom phase on my second tank not prettybut thats aquariums for ya
also ottos surprisingly prefer numbers, i would recommend adding at least 4 more, unsure on your tank size but they do stay small 2 cm max sorta size, i have 6 in my 23g and 5 in my 35g i believe, i may even get more lovely little critters tho munching on the glass 24/7 on my tanks