Chemistry Controllers For Commercial Pools

How Automatic Are Chemistry Controllers? A Comparison Of Different Technologies

In Blog, Controllers by Aaron Donohue

Every day thousands upon thousands of facilities across the country depend upon their chemistry controllers to keep their pools and spas in line. Yet despite the staggering number of devices out in the field, multiple control types and myriad of options on the market, there still seems to be a pervasive misunderstanding about just how “auto” these pieces of equipment are and what to expect from each of them.

The most common complaint I deal with regarding chemistry controllers is that they “are not working”, and upon digging just a bit further we find the equipment is doing exactly what it should, and to the level we would expect. The real issue comes from unrealistic expectation of the equipment’s capability.

Chemistry controllers are much like “cruise control” in a car, they only work if the components they depend on are also working and maintained.

Just about all chemistry controllers work similarly regarding pH, so for this blog we’ll focus on the chlorine control side.

There are a number of different types of control equipment but most fall into one of the following groups when it comes to chlorine control:

  • ORP
  • ORP with calculated ppm
  • PPM with reagent based photometers
  • PPM with amperometric sensors


Having a good idea of what the type of equipment you use is capable of will help you to make informed decisions about operating procedures and testing schedules, as well as plan for proper care and maintenance of the system. Above all else with a chemistry controller it is important to know that none are truly “Automatic” every unit requires verification by hand, and periodic (or frequent) human interface.

Below is a breakdown by control type along with their main pros and cons and what to expect from each.



ORP controllers are far and away the most prevalent, both because of the lower price point and because of the relatively simple operation.  This is their upside, they can be installed in just about any type of pool, in any type of facility and given the correct programming options, can work fairly well to make sure there is chlorine in the water. The main limitation is that ORP is effectively a Qualitative measurement where PPM is a Quantitative measurement. This means we are only able to correlate one to the other, which leaves room for error and drift. ORP it is much less precise than a PPM based system, and as such will tend to hold to a wider “band” vs. a real set “point”. When you are only concerned about “having chlorine” and not trying to hold to within 0.5 – 1 ppm, ORP should work just fine for you.

  • Pros:
    • Inexpensive
    • Simple
    • Flexible
  • Cons:
    • Lack Accuracy
    • Not fully understood by operators
    • May have limited control options
  • What to expect:
    • Expect to check the system at least 2-3 times per day, making minor adjustments as needed.
    • Expect chlorine to be about +/- 1.0 ppm of your target level.
    • Expect regular maintenance cycles of 30-60 days.

ORP with Calculated PPM

Controllers that use ORP with calculated PPM are a step ahead of the ORP only system, using the pH measured and programming algorithms, the controller “calculates” the chlorine level and displays it. These can then be calibrated and can hold to a tighter window than ORP only, but the method is still using a correlating function and can be sent off track in certain conditions. With properly programmed safety cutouts, feed limits and conditional logic; performing Regular service, maintenance and calibration will typically keep these systems running well.

  • Pros:
    • Less expensive than PPM systems
    • Flexible
    • More accurate than ORP only
  • Cons:
    • More complicated than ORP only
    • May require outside service techs for calibration
  • What to expect:
    • Expect to check the system at least once daily, making minor adjustments as needed.
    • Expect Chlorine to hold within about +/- 5 ppm of target when regularly maintained.
    • Expect regular maintenance cycles of between 30-60 days.


PPM with reagent based photometers

Reagent based PPM Based controllers have been around for a while. On the plus side, they are usually very accurate and require little calibration out of the box, they can maintain very tight windows (+/- 0.1 – 0.2 is not uncommon) and they are reliable. However, this accuracy comes at a cost. The reagents themselves are only good for a short time (usually between 20-40 days) and they are not cheap, so the operating cost for these systems is about the highest of all the options. Also, these systems require more maintenance than any other. Due to the sensitive light-based measurements, the systems must be cleaned thoroughly every few weeks. They must also have fine adjustments made after each cleaning cycle to get things back to a “baseline”, while not complicated the process is time consuming, adding to the operating cost. These systems are also limited in use, so you must work with a supplier that is intimately familiar with them to get the most out of them, inexperienced suppliers will not be able to provide insights and help you avoid the pitfalls that come from this setup.

  • Pros:
    • Very Accurate
    • Few calibrations required
  • Cons:
    • Expensive to operate
    • Time consuming & frequent maintenance
    • Not widely used, limited support knowledge
  • What to expect:
    • Expect to check the system at least once per day, making adjustments infrequently.
    • Expect accurate control down to 0.1-0.2 ppm
    • Expect higher than average maintenance requirements
    • Expect maintenance cycles of 20-30 days


PPM with Amperometric Sensors

Amperometric PPM sensors have been around for years and recent improvements in the technology have made them the “go to” for current generation PPM systems. Amperometric sensors bring the accuracy and controllability of the reagent based systems, but do not have the extensive maintenance and setup requirements. They are also generally going to be less costly to operate long term and will be used in more technologically advanced systems which bring their own host of benefits (i.e. more features, control functions, accessibility, etc.) However, they are expensive upfront purchases when compared to the other systems. The best amperometric sensor/controller combinations allow for quick setup and consistent operation for multiple months without any major maintenance.

  • Pros:
    • Very accurate
    • Simple to operate & maintain
    • Lowest operating cost of PPM systems
  • Cons:
    • Higher up-front cost than other ppm systems
  • What to expect:
    • Expect to check the system at least once per day, making minor adjustments periodically
    • Expect accurate control to 0.1-0.2 ppm
    • Expect infrequent maintenance needs

If you would like help deciding what would work best for you and your facility, you can contact us at