I have had my 75 gallon tank set up for about 2 months. I have 2 marineland emperor 400 filters on it. I did a fishless cycle to set the aquarium up. Currently have 4 guppies, 6 neon tetra, 5 glofish tetras, 1 neon blue dwarf guorami, and 6 zebra danios. I have been doing regular water changes and just noticed that there is brown algae over the bottom rock, fake plants, and decorations. It has popped up in the last couple days. It might be diatoms also. I have a LED light that has been on for about 12 hours a day. Water has been tested and ammonia 0, nitrite 0, and nitrates 20. ph is 8.2. Any suggestions on how to get rid of the brown algae? Do bottom feeders or shrimp help? Thanks for any help you can provide.