Nutrient lockout is a common problem in hydroponic operations. Even when nutrients are available and perfectly proportioned for the needs of the plants, if the plants cannot access those nutrients, they will suffer from poor growth, vulnerability to stress and even disease, and limited productivity. Imagine looking at a table laden with food that you can't get to. The food is there, but useless to you.
Nutrient lockout usually happens when pH levels in the nutrient solution are too high or too low for that particular crop. It can also happen when the media is saturated and fresh solution cannot pass into portions of the media where roots can reach, or when an imbalance of nutrients has built up, leaving too much of one element and insufficient amounts of others. Early warning signs include leaf yellowing, leaf curling, and weak or stunted growth. If you see these signs, the quickest fix will be to replace your reservoir water and clean out your system, ridding it of built up nutrient salts. To avoid such a problem from developing, check your solution's pH regularly - daily is not too frequently - and always after adding a new dose of nutrients or topping off with water.
