Lock-out occurs as a result of overfeeding, which is the most common mistake made by beginners to hydroponic gardening — more is definitely not better where hydroponic nutrient solutions are concerned.

If the nutrient solution becomes too strong, that is, the conductivity level gets too high, then some elements in the solution will bond together. This results in them becoming ‘locked-out’ and unavailable for use by the plant. For example, plants need and use both calcium and phosphorus but when these two combine to form calcium-phosphate, the plant cannot access either nutrient.

Therefore over-feeding the plant (or letting the conductivity level get to high) will lead to a deficiency of nutrients and not an excess. This careful balance of the nutrient solution is the ‘art’ of hydroponics.