Talk to any experienced grower and they will tell you that one of the most important features of their grow is the ability to control pH. pH (which, as most people are unaware, stands for "potential Hydrogen") is of paramount importance to any hydroponic/soil grow operation because it affects the way that nutrients are absorbed into your plants. Many growers have long had an adversarial relationship with their nutrient solution's pH, but recent advances in nutrient technologies have made pH much more easily balanced within the nutrient reservoir, without the need of buffer solutions like pH up (an alkaline solution) or pH down (an acidic solution). Here is the lowdown on pH, how it affects your plants, and how you can keep it in that "sweet spot" that plants love.
Why pH Matters:
All green-leaved plants can survive just fine with a pH between 4.0 and 7.0. Basically, because the plants are made of relatively weak acids, they enjoy an environment that is also on the acidic side. However, when you are growing hydroponically, the nutrient solution that you provide to them is their life force, and nutrients will not be absorbed properly without the solution composed of the correct pH.
While the optimum pH for plant uptake may vary from one mineral to another, experts have determined that the optimum range for most of them is between 5.5 and 5.8 (DWC) and between 6.5 and 7.0 for soil, though many growers will argue that anything up to the 6.2 range is perfectly fine for hydroponics.
Minerals like Manganese (Mn), Copper (Cu), Zinc (Zn), and the especially critical Iron (Fe) have reduced absorption rates at a higher pH, while Phosphorus (P), Potassium (K), Calcium (Ca), and Magnesium (Mg) have issues being absorbed at a lower rate. This doesn't mean that no nutrients are absorbed at higher or lower pH levels, but why waste valuable nutrients because your roots essentially don't know that they are there?
Controlling pH
There are a variety of tricks to keep your pH balanced. Firstly, for God's sake, make sure you have a meter, and a good one. My advice to growers is that nutrients, meters, and lights are not the places to save money. Spend some dough on a great tri-meter (pH, ppm, and temperature), and you will have the best chance of knowing what is happening in your reservoir.
Also, invest in some simple aerators to keep the nutrient solution in your reservoir constantly circulating; this will add oxygen to your solution (which makes roots happy) and make sure that all of your nutrients are evenly distributed. Aerators are inexpensive and can be purchased anywhere from hydro stores to pet stores, and even Target or Wal-Mart.
To keep pH within that optimum range, growers have traditionally had to rely on buffer solutions, like pH up and down. While relatively inexpensive and incredibly effective, these buffers add unnecessary particulates to your reservoir, often causing your ppm meter to register a higher number than it would if it were only measuring your nutes (like it should). They are also extremely caustic and burn like hell when they come in contact with skin, especially both at once.
One trick of the trade that is lesser known and less commonly used (though can be effective if you know what you are doing) is to add excess levels of Phosphorus (P) to your reservoir. Because of the way that it interacts with the other nutes, it will work to keep your pH at an optimum level (for a while). The downside of this technique is that as you use the nutrient solution in your reservoir to water your plants, and it recycles back into the reservoir in a never-ending cycle, your plants will uptake not only the nutrients that you mixed for them, they will absorb that extra Phosphorus as well. So, when using this technique, the efficiency drops as you water your plants – nothing will be as accurate as a brand-new, freshly mixed reservoir.
Changing the Game
While the info here will allow you to have a successful grow and harvest (providing you do everything else correctly), it takes time, effort, and constant monitoring to keep pH at an acceptable level to your plants. Your little green buddies will absorb nutrients at different levels during different parts of their lifespan (veg vs. flowering), so your pH will be constantly changing, and not always in the same direction. It takes a dedicated grower (or an automated system) to stay on top of this.
] with alkalinity. Other laboratories assume that bicarbonates are the sole contributors to alkalinity.
