What are the general causes for plants dying off? I have 2 tanks, and the same exact plants in both tanks. Water and treatments are the same in both tanks, yet in one tank, the plants are dying and in the other they are not. The only difference is that in the tank where the plants are dying, my fish suffers from constipation. He is fasted often as a result. In the other, my fish is a pooping machine and has NEVER had a problem with constipation. In the dying plant tank, after a week (I change the water weekly), there is hardly any poop to suck out. In the healthy plant tank, there is tons and tons of waste. They are both cycled tanks and readings are normal.
Both tanks are identical, they have the same LED lighting. There is no natural sunlight in that room - direct or indirect (the only room that gets natural lighting has a window right next to the door, and is single-paned, so in the winter, it gets well below freezing by the window and in the summer, can get up to 90 or hotter - not a good spot for fish at all)
Could the lack of fish waste be a factor here? And if so, would fertilizers help? Which fertilizers are good to use?