"Leggy" stem plants

I was wondering if it's only my setup that has this syndrome but many of my stem plants seem to be growing extremely fast to the point where ambulia has like 2 inches of stem between the leaf nodes and the rotala.macrandra shows similar symptoms but nowhere near as much.

In my opinion, the ambulia would have looked better if it had more dense leaf structure. New shoots are appearing every day and they start off looking normal but once they reach 12" or so in size, they seem to grow the same way as the rest of it.

All those plants are pearling within 2 or 3 hours after the lights come on and all broad leaf plants seem healthy with solid green colour and slightly visible veins.

It was suggested to me that this might have to do with high K relative to N so I dosed a bit of extra KN03 but since doing that, the rotala.macrandra shows some grey spots on the leaves and doesn't look quite as good as before.

I had always thoughts this was consistent with low lighting but the ambulia shows these symptons as much directly underneath the halides as elsewhere.
I have 3 x 150W halides (10,000K) on this tank plus another 100W of fluoro.
(on a 180Gal tank)

Any ideas?