Dosing ferts is tricky in shrimp tanks, but with no fish feeding and producing NH4 and PO4 it has to be done to keep plants in top shape. I use Green Leaf Aquarium's dry ferts (mentioning them since you're in America). But you can't risk running a full EI dose with sensitive shrimp, you kind of have to tailor it to their needs. I try to keep nitrate and phosphate just showing on a liquid test kit, and add potassium and trace with every water change. How much will be needed is largely determined by plant mass and lighting -however much they are growing, they are using. But long-term stability? Nothing beats an old mature tank. An aquarium can be said to be cycled in as little as 3-4 weeks when no ammonia or nitrite is showing and nitrate is. But a healthy 2, 3, 4, 10 year old tank is just such a different beast. Ever find a dead fish in a newer aquarium covered in a cottony fuzz? In an old aquarium, that same fish is decomposing into skeletal matter. There are all manner of tiny microorganisms that we can't see that do a lot of work we can't measure on a test kit. Or perhaps we could with measurements like ORP and such, but those aren't popular in the freshwater side.