Hello Pal, I'm not saying it isn't iron, I'm not that experienced at spotting deficiency, I actually have some myself at the minute in my tank which also looks like iron def but one thing I know it probably isn't is nitrogen. My reasoning is I dose E.I levels of nitrate and I have floating plants that are thriving. Floating plants tend to show up first any nitrate issues because they are closest to the light, are in a co2 rich top layer and love consuming nitrogen. That's my tank though so back to yours.
The figures I used are from rotala which I linked further up. Put your tank size in and what fertiliser you are using and it outputs the totals of each nutrient. I've highlighted nitrogen and dose. As you can see if you added 35.7ml of Trop Spec which rotala recommends to get your iron level right which is also the bottomn end of the scale when it comes to ei levels of Iron (see image 2) then you would be adding 3.83ppm of nitrate. Knowing your tank, how much plants and co2 with your lighting this is quite low I would have said. EI values range from about 20/30ppm of nitrate.
You dose 14 pumps or about 17ml of tropica spec, which is half of that, forget the premium it has no nitrate in. The premium will up your iron though. So considering tropica uses a good chelator for iron in your harder water chances are you might be low on iron but almost certainly v low on nitrogen. I've followed a few threads on people who have used Tropica only products and the general census of opinion on them is that they had to massively increase the dosages when combined with high lighting to the point it wasn't financially viable.
These are just my opinions though, so please anyone with more experience jump in. The thing is you have some kno3 so it doesn't do any harm IMO to give a little a try. Failing that yes, iron could be in the frame but my gut feeling is it would be suspect number 2.
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