Picture of Build Your Own Spa or Pool Monitor
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Cropped Cosm print screen SpaSitter 2.0.png
hot tub photo.jpg
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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.

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

bhuebner (author)  mcaskey111 hours ago

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

DavidF33 months ago

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.


timm.tanner2 years ago
Great build. Can you share a source for the two probes? Thanks.
bhuebner (author)  timm.tanner2 years ago
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 !!!!
bhuebner (author)  acampanella11 year ago
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...
anjoze12 months ago

Hi. Thanks for your tutorial.

Can you please detail the calibration procedure. Thank you

78081 year ago
how much did you spend on the probes? how much total? thank you (i will price out my self too, not that lazy, just curious)
Hello. I'm still a novice in this kind of stuff. i would like to know if the Nanode can be replaced by a cheaper Arduino boards?? and speciically what board? thanks :)
bhuebner (author)  phersuasion1 year ago
It can be replaced by a combo of an Arduino board and an internet enabled shield. Specifically there is not an exact board, many will work. Join our forum here to view some other project builds posted that you could use as examples.  We would be happy to help you pick out the correct equipment for your needs. 

dbaker231 year ago
This is awesome! Would it be possible to make this kit powerable using Power Over Ethernet?
bhuebner (author)  dbaker231 year ago
Yes! The first version I made used a Power Over the Ethernet Shield. It is still being used and works great. I used this board: .  I was able to use the proto board on the freetronics shield for the temperature probe circuit.