Aquarium Changes

There has been many changes to my aquarium during this nine weeks. First of all, originally, I had perfect a nitrate level but had high ammonia. Once we added fish  and bacteria to the aquarium, our ammonia levels dropped significantly. However, once we had a buildup of feces and one of our fish died, our nitrate level increased dramatically. To reduce this, we added plenty of duckweed because plants absorb nitrate. After some time, our water started to turn brownish but our water quality tests always turned out good so I saw no reason to change it. There was some algae growth on Squidward's house and on the fake plants, but other than that, there was no plant growth.