If the wisteria is healthy, what is most likely happening is the anubias is being out competed for K (or nutrients in general). So you're going to have to reach unlimiting levels globally, in order for the slow growers to have enough left over.
Think of a pack of hungry lions on a fresh kill. The strong are always going to get theirs first. The weak often have to wait for what is left over. So in order for the anubias to eat, so to speak, you need to make sure there's always some left over.
Yes. Exactly. I just don't want so much left over it creates unhealthy water for the fish, so I'm trying to ease UP to the right amounts, treating deficiencies as I see them.
Maybe that's a bad approach. But so long as the plants look healthy and I get a balance, I do not much care which nutrient is the limiting one, including light. Though I guess light and/or CO2 are the ones that cause the least visible issues with the plants.