It is right at 2 years old. Ammonia 0, nitrite 0, nitrate 0, phosphate 0, KH 3, GH 2, pH 7.
The black stuff is on the plants and rocks.
The light is on for 1 hour in the morning and 3 hours in the evening.
Removing the affected growth is tantamount to removing all the plants. And yeah. I...