He doesn't have a nitrogen problem, that much is very clear from the picture. He has a nice yellowing that is gradual and the fan leaves look great being all yellow uniformly and not burnt tips or middles. This yellowing is simply from the plants flowering cycle. You're plants have great color. Honestly looks like you just need to start flushing. Container plants will always fade sooner than earth planted plants, always. Especially when you're container is to small. Start letting your plant dry out more and more between these last waterings..
