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Understanding pH and PPM in Hydroponics

What is pH and PPM and how do they affect your cannabis growth

In the world of hydroponics, particularly in Recirculating Deep Water Culture (RDWC) for cannabis cultivation, the success of your harvest can be maximized by the proper balance of two fundamental factors: pH and PPM. These acronyms are thrown around quite a bit in the cultivation industry, but actually understanding their significance is key for any grower looking to achieve high volume and healthy yields.

What does pH Mean?

pH stands for the potential of hydrogen ions in your water, essentially determining whether your water is leaning towards acidity or alkalinity. This factor plays a pivotal role in cultivating healthy plants time and time again. The key is finding the sweet spot — not too acidic, not too alkaline.

pH Scale

What does pPM Mean?

PPM, or parts per million, delves into the concentration of minerals and soluble matter in your watering solution. This metric provides insight into the nutrient density your plants are receiving, directly impacting their growth and vitality.

PPM Formula

Why do pH and PPM Matter in RDWC?

Imagine them as the backbone of your grow room or tent, supporting the foundation that your plants thrive on. Balanced pH and PPM levels are not just optional; they are the primary source of cultivation success. The difference between a robust, flourishing harvest and weak, sickly plants often boils down to the meticulous management of these two parameters – negating other outside factors.

The pH Balancing system

Too Low: Toxic Territory – A pH that dips too low can create a toxic environment that will harm or kill your plants. It's a red flag that you don't want waving in your grow space.

Too High: Stunted Growth – A pH that soars too high can impede nutrient uptake, resulting in stunted growth. pH levels that are too high also run the risk of harming and killing your plants.

Optimal pH for Cannabis Chart

What pH Should I have for cannabis cultivation?

The magic number? There is no such thing. Just like people, each plant is unique. However, after much research and testing, it is safe to aim for a pH range of 6.0 to 6.5 where a majority of plants will thrive. This narrow window provides the ideal conditions for nutrient absorption, ensuring your plants can effectively break down and utilize the essential elements they need to thrive.

How to Measure pH in RDWC

There are a few ways to accurately measure your pH in an RDWC system. One way is to use the paper pH strips available online or in many retail stores. These are a good way to get a general idea of your pH levels and are very cost effective to start, but don't quite give the accuracy needed for professional cultivation. Another method, that we recommend, is picking up a digital pH meter that can determine the exact pH of your solution and provide you a concrete number value. When measuring pH in a HydraMax system, the value will be the same or close to the same all around the entire system, so you can check one bucket with your pH meter. When using other systems, we recommend checking ever couple buckets to get an average pH value of the system.

What PPM Should I Have For Cannabis Cultivation?

The PPM value will vary for different stages of growth. During Vegetative growth it should remain around 400-450 PPM. Once your cycle is in the flower stage of growth, the ideal values vary and should be constantly monitored to maximize your yield. The following is a general schedule during the flower stage that can be treated as a baseline; adjust accordingly based on your nutrients recommendations.

  • Flower week 1 – 450 PPM
  • Flower week 2 – 500 PPM
  • Flower week 3 – 650 PPM
  • Flower week 4 – 750 PPM
  • Flower week 5 – 850 PPM
  • Flower week 6 – 910 PPM
  • Flower week 7 – 850PPM
  • Flower week 8 – 500 PPM
pH value for flower stage of growth

Be sure your equipment is properly calibrated!

Cultivators must calibrate their pH and PPM meters diligently. Accurate readings are non-negotiable. We emphasize the importance of employing multiple testing methods to cross-verify readings, offering you a reliable and precise measure of your water's pH and PPM.


In the world of hydroponics, precision is not a luxury; it's a necessity. By mastering the art of managing pH and PPM in your RDWC cannabis grows, you empower yourself to create an environment where your plants can flourish, resulting in a harvest that truly reflects the potential of your cultivation expertise.


Looking for more information about best cultivation practices? Our Grow Guide takes a deeper dive into what is recommended for each stage of growth in a step-by-step process. Looking to maintain your pH levels properly? Check out our blog post on Maintaining pH Levels in Hydroponics! (coming soon)


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