As the tank mature you have natural decomp from organics that add nutrient back to the soil-along with all the poop/byproducts produced by the livestock...All food for the plants and to help maintain nutrients in the soil itself.
This is why you don't want to over clean a soil based tank.
Sometimes, if you have a lot of root feeder plants-like swords-they might need some extra food after about 4-5 years. I make clay balls from my native clay-allow them to dry in the sun-then cram them under/around the base of the sword plant a couple of times a year or when the plant looks tired.
Last edited by Rainbo; 03-31-2019 at 12:55 PM.