Plants growing ok. Without any nutrition some leaves began to show a light green shade. This indicates nitrogen deficiency.
I had already on hand a novice nutrient solution set. It consists of 3 bottles with different concentrations of NPK and micro nutrients. Such solutions will have a number such as 5-0-0.
The number shows the volume of N, P and K in the solution. The bottles I have are
N 5:0:0 ie N=5v/v P=0 K=0
P 1:6:0 ie N=1 P=6 K=0
K 4:0:1 ie N=4 P=0 K=1
Mixing all 3 equally in water will give you a solution with 10:6:1 ratio of NPK.
The pH for each solution is stated as N 4.6, P 4.45 and K 4.71.
Additionally the N solution contains Ca, Zn, Cu, Mn, S, Silica
The P solution contains Fe and B
The K solution contains Mn, Ca, S
The concentrations of these additional elements are not specified. Nor is the nature of the chemicals having these additional elements specified.
The amount of fertilizer - ie dissolved salts - in the water is measured by measuring the conductivity of the solvent. It is supposed to be ideally set at 1500uS for best absorption. Note that the measurement merely measures conductivity as a proxy for the above dissolved nutrients. IF one were to dissolve NaCl one can easily get the above reading without any of the plant nutrition.
Most vegetable Plants require a pH of 6-7.5 to absorb nutrients efficiently.
Ideally one should start with deionized water with pH of 7. Water from a RO filter can be used. However my setup uses tap water. The pH of my tap water is 7.5 and the EC value was 200uS.
Mixing 10ml each of the above solution in 1 li of tap water changed the EC to 1500 and pH to 6.8.
We now have a fair idea of the mix ratio. My tank hold 7li. So approx 70ml of each should get me an EC and pH in the required range. Mixing 70ml into the tank produced the desired results.
A day later the pH rose to 8.2 and EC dropped to 700uS.
Adding 40ml of NPK raised EC back to 1600. But pH dropped to only 7.5. We added 3ml of lime juice, which dropped the pH to 7.2. We continued adding a few drops of lime juice until pH reached 6.5.
Today I measured EC again. It had again dropped to 700uS and pH to 8.5. Which means the plants are absorbing the nutrients. Repeated the previous days process, but replaced lime juice with apple cider vinegar.
The liquid nutrient solutions are way more expensive than solid nutrients - we are paying for water.
The nutrient mix compositions revealed by the all knowing google/duckduck have innumerable recipes. Will have to read more on the topic.
MEasuring pH and EC everyday is a bit of a chore. Would be nice to automate the measurement and nutrient adding. I will require 4 containers with N, P, K and micronutrients and 4 dosing pumps. I will also require pipes and valves for routing nutrients to appropriate towers depending on what is planted and it’s growth cycle.
Fun days ahead.