How do I determine if my hydroponic nutrient solution is the right concentration for my plants?

Most hydroponic fertilizer companies will include application directions in their product literature that are broken down by specific plant sizes and stages of development, but there are steps you can take to ensure your plants receive adequate nutrition. Frequent EC measurements will help you determine whether the nutrient solution in your reservoir is too strong or too weak for your crop.

If the water level in the reservoir drops relatively quickly and the EC measurements rise, then the solution likely contains more nutrients than your crop requires. Make adjustments by adding purified water until the EC levels out. If the water level in the reservoir drops relatively slowly, but the EC measurements fall at a fast rate, then the nutrient solution is likely too weak to meet your plants’ needs. To remedy this, add nutrients at half-strength until the EC stops dropping to help even out water-to-nutrient consumption rates. When the water level drops at a more normal pace, depending on plant sizes, and the EC measurements stay stable the whole time, then the nutrient solution is at the right concentration.

Finding the sweet spot for the nutrient solution strength may take some trial and error, but you will know when it is reached because the EC measurement will stay steady as the solution level in the reservoir drops. The sweet spot may also fluctuate as plants grow and require greater amounts of water and nutrients. If you want to top off the nutrient reservoir so it maintains a certain level, simply fill to the desired level with purified water and then add extra nutrients until the desired EC measurement is reached once more. Some growers will use a nutrient solution mix that is one-third to one-half the suggested concentration to top off reservoirs. A top-off solution is a great way to maintain a consistent EC measurement. Macronutrients like nitrogen will be taken up by plants at faster rates when compared to trace elements like copper.

To avoid excess accumulations of trace elements, the nutrient reservoir solution will occasionally need to be completely replaced. A good way to ensure the solution is changed frequently enough to avoid complications is to replace it after the total volume of the reservoir has been replaced through topping off. For example, if the nutrient reservoir is 5 gallons and it is topped off with 1 gallon every day, then after five days, the solution should be completely replaced with a fresh mix. I highly recommend reading all the literature the hydroponic nutrient company has to offer before starting a grow cycle to determine suggested rates. This will give you a good idea of where to start and small adjustments can be made from there.