ppm ferts for cloudforest orchids

[Tonio]

for my wabi kusa wall project I try to find the right amount of ferts.

Among other plants on the wall some cloud forest orchids will grow. What I understand from reading here and on the www is that they like to be fertilized on the lean side.

But I need some advise on how low I should gow.

In my setup plants are always exposed to the tank water and the ferts in it.

Once a week I change about 30% of the water, minerals and fertilizers will be added to a certain level to the fresh water before it is added. By only fertilizing the new water there can't be fertilizer build up over time. the levels I add are the maximum levels.

what I have now:

NO3 6 (N 1.35538)
PO4 0.5 (P 0.16307, P2O5 0.37367)
K 6.52567 (K2O 7,86147)
Ca 4.37853
Mg 2.81696
S 2.17
Fe 0.2
Cu 0.01067
B 0.02667
Mn 0.05333
Mo 0.00267
Zn 0.01067
Na 0.04333
Co 0.00013
Cl 0.01433
Al 0.00003
Ti 0.00003
Ni 0.00003
I 0.00003

HCO3 10.15
Acetate 12.44

TDS 37 (calculated)
GH 0.67 DH
KH 0.47 DH

Iron and other micro nutrients will be OK I think.
My concerns or with the macro nutrients.
Nitrogen is to low maybe?
Potassium is quite high (compared to NP) the majority is coming from potassium bicarbonate, and I need the bicarbonate part to buffer pH if dosing co2. The alternative is sodium bicarbonate. And sodium is useless.