I'm showing this graph to explain some of the questions raised on pH and EC:

This graph is about some pring onion seedlings in an ebb&flow system.

The pH started off a bit high, and was adjusted over a few days until it reached the lower reading of ±5.3.

While this happened, The EC of the nutrient steadily increased from about 1600 to ±1800. The seedlings were obviously drawing water

But then the pH started to rise, which suggests that the seedlings were also drawing on the nitrates.

THe rises in pH and EC were slightly disturbed by some overnight rain, which diluted the nutrient somewhat, but then - when the pH rose above 5.7 - I made an additional adjustment with some 5% nitric acid, AND, I added some RO water to dilute the nutrient, which had risen to ±2000.

The story then starts all over again:

The onions are growing, requiring nitrates, and the EC is rising because the plants use more water then nutrients.