You seams to have a algae problem to. Well here are the things i did to fix it. If you have spots green algae on the window . The reason for that, its to mush light. Indirect light from window do contribute more then you probably think.
You and i have a 30 gallon tanks. Interesting fish to clean the windows, that are fun, is the smallest pleco bridgestone 3 inch. You may add 3 ottos minimum. Real fun to see them clean the plants. I do enjoy my crystal shrimps, you need a min of 8 for the size of your aquarium to see them in action (hiding all the time), a bit expensive here in Quebec at 10$ a pop.
If you have plants, the reason you have algae its fertilizer imbalance.
For fish, transparency tetra are pacifist and cool to look at. Still its you decision to make on that one.