Build Your Own Spa or Pool Monitor





Introduction: Build Your Own Spa or Pool Monitor

Anyone who has owned a hot tub knows that without keeping a close eye on the water with test strips and water test kits, a hot tub can quickly become green, cloudy, and unusable.  A pool can often be just as hard to manage.  Monitoring the water chemistry 24/7 and alerting you when chemicals need to be added is invaluable to managing the water quality in your spa.  This was my motivation behind the SpaSitter, an open source spa or pool monitor using a Nanode (an Arduino based network enabled node) and 's easy graphing API and triggers. Now you can always have easy access to your water conditions on your smart phone or the web.  Set up email alerts to notify you when water conditions start to degrade.  

Remotely monitor pH, ORP (Oxidation Reduction Potential), and Temperature
More documentation can be found at the OpenSpaMonitor blog.

List of Tools: 
Solder iron 
Wire strippers

List of materials: 
Nanode Classic or better with Optiboot loader - Developed by Ken Boak and the London Hackspace 
2 -  Phidget 1130 ph / ORP adaptors
pH probe with BNC connector (preferably industrial grade probe)
ORP probe with BNC connector  (preferably industrial grade probe)
waterproof DS18B20 temperature sensor
4.7K ohm resistor 
Bread board or proto board for temperature sensor
5V power supply for Nanode (AC wall adapter or Batteries)
FTDI cable (USB to serial converter to program the Nanode)
Long Ethernet cable or Ethernet over power-line adapter
Waterproof project box
pH 4 and pH 7 reference solution (optional but recommended) 

Make the SpaSitter 2.0 for web-based monitoring of water chemistry in swimming pools, hot tubs, aquariums and other bodies of water.  We have spent over a year testing the continued use of the pH and ORP (Oxidation Reduction Potential) probes in a hot tub environment. They have remained very accurate and react well to changes in water chemistry. These high quality industrial grade probes are expensive, but they will outlast any cheap commercial monitor. They can also be reconditioned and calibrated as needed.  The cheaper 30 dollar pH and ORP probes worked for a couple months,  but are not suitable for extended use or hot conditions.

Its easy to use!  Drop the sensors into the water and put the electronics in a waterproof project box.  Run a Ethernet line out to the monitor and plug it into a power supply.

Step 1: Build Your Nanode

Assemble your Nanode 5 with an Opti Boot Loader 


Nanode RF with no RF module

If soldering isn't your cup of tea, you can buy pre-assembled Nanode boards.

Step 2:

Build a temperature shield with the water proof DS18B20. Use digital pin 8 on the Nanode as the one wire input pin.  The red wire is 5V power, black is ground, and yellow or white is digital input.

A breadboard or proto board can be used for this step. 

Step 3:

Solder the Phidget 1130 pH and or ORP boards (Wiki: to the Nanode board.  Red is 5V, black is ground, and white is the analog input.  You can cut down the long phidget 1130 wires and strip the insulation off the ends.   Combine the red wires together and solder them to the outer 5V pin.   Do the same for the black wires and land them on the ground pin.

Analog Pin 0 is the pH probe input, analog Pin 5 is the ORP probe.  Solder them on the outer pins of their respective place. 

Connect the pH and/or ORP probe to the Phidget 1130 board.  Select the correct setting by moving the indicator switch,  make sure the pH probe is attached to the pH board and the ORP probe is attached to the ORP board.  There is a little toggle switch on the board that indicates if the board is used for pH or ORP.  

Add the temperature sensor that you built in step 2 to the Nanode.  

Step 4: Edit and Upload Your Code

Now its time to put it all together.  Setup a account.  Here is a great tutorial at Adafruit Learning System.

Download the Arduino IDE software:

Download the sketch for the Nanode at github:
* Code adapted from the  authors Trystan Lea and Glyn Hudson
** Note, you need an FTDI cable for uploading the sketch to the Nanode

Add your feed ID and API key to the part of the sketch referenced in the image. 

Using your FTDI cable, upload the sketch to your Nanode.

Step 5: Calibrating Your Probes

Get some standard reference solution for you local hydroponics grow store or from a chemical supply site.  Also fill a spray bottle with distilled water for cleaning the reference solution off of the glass probe junction.  Do not touch the glass probes with your fingers, as it leaves oil residue that will influence your reading. Also, always be sure to rinsed the electrode thoroughly with distilled water only when calibrating. 

Two calibration points will be fine: pH 4 and pH 7. Though for better accuracy, use pH 10 as a third calibration point.  Get two glasses (or three if you use a third calibration point) the kitchen and rinse them with distilled water. Add enough reference solution so that the glass probe will be fully immersed in the solution.

Place the pH probe in pH 4 solution and wait one to two minutes. Using the serial monitor on the Nanode, read the output of your pH probe (un-comment out the #debug  serial.print function) . Write down this value. Remove the probe from the pH4 solution, rinse the glass junction thoroughly with distilled water and then place the probe into the pH 7 solution. Allow the reading to equilibrate as before and record the output. Repeat the process with the ORP probe. 

The ORP probe in the pH 4 reference solutions should read around 740 mV and the pH 7 reference solution should read around 580 mV.

Now that your probes are calibrated and your SpaSitter is tested and working, its time to install it.  Run an Ethernet cable and power supply out to your  hot tub, pool or other water body and put it all in a water proof project box.   Have fun with your new SpaSitterTM.   Setup email or text message alerts to notify you when the conditions of your water need attention.  Add the widget to your smart phone for easy access to your SpaSitter.



    • Planter Challenge

      Planter Challenge
    • Woodworking Contest

      Woodworking Contest
    • Oil Contest

      Oil Contest

    We have a be nice policy.
    Please be positive and constructive.




    Can someone update this project? It appears that the Nanode is no longer available. Can something else be used in its place?

    Does anyone know where to obtain a Nanode? Can this project be completed with a Raspberry Pi? Sorry for the redundant questions, but I want to confirm before diving into the project as a noob. In reference to galvanic isolation, should an isolation shield be used (such as Atlas Scientific Tentacle Shield Mini). Would the codes be the same? Also Cosm is no longer free, can lively be used instead? Code change?

    Thank you for your patients with these questions.

    I seem to be having some trouble sourcing a nanode (kit or complete). Is there a suggested alternative?

    3 replies

    Here is the Nanode shop:

    Also check out .. you could use there Raspberry Pi for a base station.

    Thanks for the info. It looks like the nanodes have sold out from the nanode shop. I will take a look at the pi option - would the programming be similar? Have you ever considered pairing this with a salt-water chlorine generator for a fully automated system (excluding pH maintenance of course)?

    Here is the Nanode shop:

    Also check out .. you could use there Raspberry Pi for a base station.

    Hello Bhuebner,

    My name is Om Suchak and I am 12 years old from New Jersey. I love building Arduino projects. This summer, I built a arduino-controlled segway. I am planning to build the SpaSitter. I read all of the links off of your blog. This link -->

    has a primer that specifies the sensors. It contains a warning that says two sensors in the same liquid could interfere with the results of the sensors. Do you think it is ok to put both sensors (pH and ORP) in the same pool?

    I look forward to working with you to build this project!

    Thanks, Om

    1 reply

    Hi Om,

    Excellent research about the sensors, I did not know that. I am not an expert on this, and I don't know how much interference they would cause each other. From my experience they worked excellent together and gave great indications that attention was needed to maintain water quality. I guess it depends on the accuracy that you require. I wanted to let you know that there are much better base stations now. Before you start, check out open energy monitor. They have put in a ton of work and improved the design and reliability. This project was based off an old design of theirs.

    anyone want to build this for me? I will pay for everything

    1 reply

    I can if you buy enough for two. Or make a donation to my local food bank. What ever the rules allow

    I love this idea. I have a question though. How often do you need to calibrate the sensors?

    Do you think this could be extended to also control the heat and chemicals, automatically, and on-demand?

    2 replies

    Yes, I think it could be. Heat would be harder, you would have to hack the circuit board in your spa.

    It actually wouldn't be too hard. Most spas and pool heaters have a built in I/O header for remote control interfaces. I know my Max-e-therm has one. The troubleshooting and repair manual shows how to interface with it, and what type pulses are required for digital logic control.

    Ay up,

    I am very new to this setup and I am very willing to build one of your project for my onground swimming pool. I notice that you use to build is Nanode, I was wondering if it will work with Arduino UNO?? As I got three of em so I hoping I can use one for this monitor project?

    Would you be kindly to let me know.


    Great build. Can you share a source for the two probes? Thanks.

    4 replies

    Thanks,  I really appreciate that.  The pH and ORP probes make up about 65% of the total cost of the project unfortunately,  more when you include the Phidgets 1130 boards.  Buying the more expensive industrial probe is defiantly worth it in the long run, unless your building it for an aquarium or something indoors and lower temperature. The two probes and hardware adapter can be found at .    I am trying to determine interest in the project and stock kits.  If people like it I'll start a wireless RF version and incorporate the pHduino.

    Let me know how your build goes.   I think you will be very satisfied with the end results.   Follow my blog for updates.

    A RF version would be awesome !!!!

    I have the beginnings of an RF version. A few people are discussing the project at Join us!

    Hey bhuebner,
    Will this monitor work with a salt water / bromine therapy pool?? I am looking to add a heat exchanger to heat the pool with a solar thermal system but using a heat exchanger means I need to keep a much closer eye on the water chemistry & your set up sounds like it would be perfect... Please let me know if it is possible to monitor a salt water / bromine pool...