Not compensated by fish and water column, because it is a very heavy root feeder. I have the same problem with my lemon plant in the garden, but it is parasite-induced. Maybe it is an aquatic analogue? Have you disinfected the plant properly, before it went into the tank. And if so; how?Thank you all for your answers. I'm puzzled, because deficiency shouldn't be possible because of the roottabs (and would show on other plants?). Too little organic material, maybe, because I was very careful on the soil so there probably isn't that much. But wouldn't that be compensated by organic waste of plants and fish? And wouldn't is show on other plants?
And sodium, there is not that much in my tapwater so where would that come from? Is there a way to measure it?