[jerryuk]

AFAIK API only provide a weekly dose amount which is 5ml per 40L, which adds 3.75ppm of K per litre. This is quite a lot higher than many other ferts but isn't particularly high given the Fertilator's recommended level of 10-20ppm.

 

[jerryuk]

Well you don't say how much Leaf Zone you're dosing but I'd hazard a guess that K isn't the problem - I'd say it's more likely that you're depleting another element and the water changes are adding it back in. If you look at PMDD recipes the amounts of K are quite high. If you're plants aren't using much then they won't be using much of anything else either.

Look forward to seeing the results of your new trace.

Jerry