Green and Brown Spot on the glass

I have 18 gallon fresh water tank (i.e. L = 22inch, D = 10.5inch, H = 18inch) with FloraMax substrate and filter capacity is 800 l/h . My tank is establish from last 5 months.

My stocking is

1. 3 Gosht Shrimp
2. 2 Amano Shrimp
3. 6 Cardinal Tetra
4. 5 Guppies
5. 1 Blue Dwarf Gourami

I have some plants are

1. hair grass
2. Java moss on dog wood
3. Anubias nana
4. Cabomba Caroliniana

I am dosing daily seachem liquid fertilizer as per Seachem Dosing Chart. Due to seachem fert my anubias nana florish with new leaf and hair grass is doing well. I am keeping my lights on for 8 hr a day

I change water every week 40-50%. Today I did 80% water change to clean tank by scrubbing glass with cotton cloth and now it is clean.

My lights are LED light on the hood of the tank. I don't know what is watt per gallon as it is not written on it.

Last week on the bottom of the tank glass is start covering with brown and very small spot of green. I feel issue is over feeding. So from today I will feed every next day. Other thing I feel is light is not good, So I like somebody here suggest which light is good which I can put on my hood.

Please also suggest me please more what can i do it will not occur again