Exactly. N,P,K are the basic macro nutrient that are need by plant to grow.
By limiting either one element, the nutrient uptake will be inbalance. Thus it is important to introduce all three macro to the tank.
If you are dosing KNO3 and KH2PO4, meaning you are already dosing NPK.
N (from KNO3), P (from KH2PO4), K (from KNO3 and KH2PO4).
Now, I believe Cruise Control question is, whether the K level is sufficient from these elements. Do we need to add another source for K.
Yes, you can add. Won't be any harm if you overdose K. But unless you notice any sign of K deficiency (holes in leaves, etc..), one really seldom need to add EXTRA K.
In special cases, where the gH is too low (gH<3), one can add K from another source (K2SO4, etc)
I haven't done any experiment on these findings. I read from people who had done it, and have great results. Diana Walstad and Tom Barr's method a bit different. One is lowtech setup (Walstad), and one is hightech setup (Barr), however the fundamentals are the same. Without any of the NPK + Traces, plants will surely suffer.
But the real question is, at what concentration level of these elements, are consider "optimum" for plant growth and at the same time avoid algea?
