Professional Marijuana Grower


Choosing the Correct Auto-Doser

Posted November 1st, 2017 by Eric Hopper in ,

Automating a grow room offers many advantages to a cannabis grower. Lighting and ventilation systems can be automated using atmospheric controllers; keeping photoperiods, humidity and temperature all in check. Serious cannabis cultivators are taking automation to the next level by implementing auto-dosing systems which regulate the nutrient concentration and pH of the nutrient solution. An auto-doser, also referred to as a nutrient doser, is a network of equipment that helps maintain nutrient and pH levels in a hydroponic system or automated soil watering system. Auto-dosers measure the concentration of nutrients and/or pH within the reservoir and automatically make adjustments to bring these concentrations to pre-configured levels. An auto-dosing system ensures stable chemical levels, prevents overcorrecting and underfeeding, saves on labor, and avoids sudden changes in the nutrient solution parameters.

How Auto-Dosers Work

Auto-dosers inject nutrients into the hydroponic system’s water reservoir or water feed lines. They are designed to maintain precise parts per million (PPM) levels within the nutrient solution. Most auto-dosers include a controller or work in conjunction with a controller that monitors the concentration of chemicals in the solution and triggers the auto-dosing system to make adjustments when needed.

Advantages of Using an Auto-Dosing System

Like other automation tools in a cannabis garden, an auto-doser offers many advantages. The biggest advantages of an auto-dosing system for marijuana horticulturists are labor savings and enhanced efficiency due to the increased consistency in the nutrient solution.

Labor Savings

The average hydroponic grower spends 20-40 minutes each day monitoring nutrient concentration and pH levels in the nutrient solution. And then  making the necessary adjustments to keep the solution within the desired parameters. By implementing an auto-doser, a horticulturist automatically saves time and labor every day. Although it may not seem like a lot at first glance, when this time is added up over the course of an entire grow cycle, the amount of time saved is very significant. As in other aspects of life, a cannabis grower who saves time saves money. He or she is free to use that time for increasing efficiency in other areas around the garden.


Although saving time on labor is important, the biggest advantage of an auto-dosing system is increased consistency in the nutrient solution. In indoor horticulture, consistency is the key to unlocking a garden’s full potential. In fact, the biggest advantage of indoor horticulture in general is heightened control over the garden’s parameters. Auto-dosers allow marijuana horticulturists heightened control over the consistency of a hydroponic system’s nutrient concentration and pH levels. Plants respond best to consistency in all areas and nutrient uptake is no exception.

In a typical hydroponic system, the nutrient concentration is tracked by a PPM or EC (electrical conductivity) monitor. The grower normally has a desired range in which he or she wishes to keep the nutrient concentration. Daily monitoring allows the grower to make adjustments to this concentration in order to maintain the desired range. Unfortunately, the concentration and pH of a nutrient solution can fluctuate out of the desired range in a relatively short period of time. Even daily monitoring and adjustments can lead to a roller coaster ride of nutrient and pH values. In extreme situations, a quick change in the pH or nutrient concentration can cause stunted growth or even nutrient lockout. In addition to this is human error. It is not uncommon for a grower to make a mistake or to overcompensate when adding nutrients or pH buffers. Implementing an auto-dosing system reduces the likelihood of human error and leads to more consistent nutrient levels and a balanced pH for the duration of the plant’s life. Many auto-doser controllers can be set to monitor and make adjustments as often as every five minutes. With a consistent nutrient concentration, the plants will never lack what they need when they need it. A consistent pH value ensures the plant’s ability to uptake those nutrients is never compromised.

Matching an Auto-Doser to Your System

An auto-doser can be used in any size hydroponic system; although, due to the cost, they are usually used by marijuana horticulturists with larger grow facilities. There are many different auto-dosers on the market, but all serve the same basic purpose: to monitor and control the nutrient concentration and pH levels of the nutrient solution. Most auto-dosing systems can be broken down into three main parts: the controller/monitor, the injectors/pumps, and the sample reservoir.


The controller/monitor within the auto-dosing system is the “brain” of the unit. The controller/monitor is a computer that, with the use of a probe, takes readings of the nutrient solution within the sample reservoir. From these readings, the controller will determine if the solution is within the desired PPM and pH range. If the parameters are out of the desired range, the controller triggers the injectors which add nutrients or pH buffers to the solution. Once the desired concentration is achieved, the controller turns off the injectors and continues to monitor the solution.

Some controllers have set durations for monitoring and injecting, while others allow the grower to set the duration for these parameters. Although it may seem like the more often the solution is tested, the more accurate the system will be, some time should be given for the injected nutrient/pH buffer to mix with the nutrient solution. Five minutes seems to be the minimum amount of time recommended by most auto-doser manufacturers. In other words, the system should be given at least five minutes to properly mix the solution before the controller makes any additional adjustments.

Each auto-dosing system is a little different, but the most common set up is a system that can handle four different solutions for injection. This is probably because the most common hydroponic nutrients are still three-part (micro, grow, bloom) nutrients. An auto-doser that can handle four different chemicals is able to handle a three-part fertilizer plus one pH buffer solution. Typically, a marijuana grower will use only one pH buffer solution because the pH of a hydroponic system tends to swing in a single direction. Although systems set up to handle four chemicals are the most common, there are auto-dosing systems on the market that can administer eight different chemicals.


The injector or pump is the component of an auto-dosing system that injects or pumps the nutrients or pH buffer into the hydroponic system’s nutrient solution. The injectors/pumps are controlled by the controller/monitor and are triggered by electricity or by water flow. There are three types of injectors/pumps commonly used in auto-dosing systems. They are peristaltic pumps, gravity fed solenoid valves, and water powered injectors.

Peristaltic Pumps

Peristaltic pumps are electric pumps which are triggered via electricity to the pump. The biggest advantage of peristaltic pumps in an auto-dosing system is the nutrients can be placed below the injection point. This reduces the chance of a spill or an over-concentrated solution in the rare case of an electrical failure or injector failure. This also allows for much larger volumes of the concentrated fertilizers to be used which reduces labor in the long run. Peristaltic pumps are typically a more expensive option, but are usually a better long term investment.

Gravity Fed Solenoid Valves

Gravity fed solenoid valves are injectors that require the concentrated nutrient to be stored above the valve and rely on gravity to create the flow of solution once the solenoid is triggered. The controller/monitor triggers the solenoid via electricity to open, which, with the help of gravity, allows the concentrated nutrients to flow into the solution.

Water Powered Injectors

Water powered injectors are triggered by the flow of water that goes through the injector. These types of injectors also have a solenoid or pump connected to the water line. When the controller triggers that solenoid or pump, it forces water through the injector, activating the “water powered pump” within the injector and injects concentrated nutrients into the solution.

The Sample Reservoir

The sample reservoir can differ a little bit from system to system, but all are very similar. The sample reservoir is a small reservoir which holds some of the nutrient solution for monitoring. It is in the sample reservoir that the probes from the controller/monitor take the readings. After adjustments are made, fresh solution is brought into the sample reservoir and monitored again. How often the solution is tested and adjustment are made will depend on the type of system and, in some cases, the parameters set by the cannabis cultivator. Some auto-dosing systems do not have a dedicated sample reservoir, but instead take samples from the main nutrient solution reservoir.

Auto-dosers can be a valuable tool for marijuana growers. Not only can a horticulturist save time on labor, but he or she can also reap the benefits of a more consistent hydroponic system. With an auto-dosing system keeping the concentration of nutrients and the pH of the solution continuously in the desired range, a grower can sit back and watch his or her garden grow. Although all auto-dosers have the same basic function, the components that make up the auto-dosing system will impact the way a grower must set up and operate his or her system. Choosing an auto-dosing system that fits the marijuana grow room’s layout is one of the most crucial steps in choosing an auto-dosing system. Commercial growers or hobbyists with large hydroponic systems should seriously consider an auto-dosing system with a peristaltic pump as they seem to be the best as a long term investment. All in all, the number of nutrients that need injecting, the configuration of the hydroponic system, and the grower’s budget will ultimately determine which auto-doser will be the best fit.

Eric Hopper is a Professional Marijuana Grower Senior Editor.

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