Pool Gem Q & A

How does Pool Gem work? 

Water monitoring with Pool Gem is much simpler than other conventional methods. The device uses a range of  sensors which measure various factors that affect water quality. The readings taken by the floating unit are computed and wirelessly transmitted in packets of data every 15 minutes to a remote receiver, located away from the pool. The receiver will display the readings and graph the data.

What does Pool Gem measure?

Pool Gem acts as a swimming pool test kit and measures three key parameters of water monitoring, these are: pH, which is a measurement of the acidity of the water; ORP, which is a measure of the effectiveness of the sanitizer; and temperature of the water. In addition, Pool Gem can measure the level of phosphates in the water. A high level of phosphates in water can result in algae growth and high chlorine consumption.

What does Pool Gem not measure?

Pool Gem does not measure any of the following:

  • Total Alkalinity (TA): Very important, as it affects the way pH adjustments happen in the pool water.
  • Combined chlorine: This is a measure of the chlorine that has combined with organic debris within the pool.
  • Total chlorine: This is the measure of free chlorine (tested by Pool Gem) and combined chlorine.
  • Cyanuric Acid stabiliser (CYA): Proper range ensures that sanitizer effectiveness (ORP) will remain high enough to protect swimmers during sunlight hours. If the Cyanuric Acid levels are too high (over 50 ppm), it will “bind” the sanitizer, rendering it ineffective. In addition, ORP sensors, such as the one in Pool Gem, does not function properly with Cyanuric Acid levels over 50 ppm.
  • Total Dissolved Solids (TDS): This is a measure of all solids dissolved in your pool water.

*But you are still advised to test for these, at intervals recommended by your pool professional.   

What is ORP and what relationship does it have with ppm chlorine?

The ORP measures the sanitising capability of the water and gives readings in millivolts (mV). The built-in software in the microprocessor will convert the ORP measurement into free chlorine (FC) reading in parts-per-million (ppm). The effectiveness of ORP as a sanitiser will decrease if the pH goes above 7.8.

Why does ORP go up during the night and down during the day?

Because during the night, with no UV light the chlorine does not bind to the cyanuric acid well, so more is available to sanitise the pool, and so the ORP will be higher. During the day, the UV light will cause the chlorine to bind strongly to the cyanuric acid and so the ORP will go down. This is why continuous water monitoring is essential.

Why does ORP go down after the pool has been in use?

Because active chlorine is being used up to keep the pool correctly sanitised

Does Pool Gem provide dosing information?

Yes; Pool Gem will provide information on how much sanitising dosing chemicals to add, if the chlorine levels displayed on the Pool Gem receiver falls below the lower limit which makes water monitoring much simpler. You can preset the limits and dosing type used, which is commonly stabilised chlorine in either dichloro tablet of trichloro granule forms.

Note: Pool Gem does not provide information on dosing for pH correction. Pool Gem does not provide dosing information on how much phosphate remover to add, if required.

How do I calculate the volume of my pool?

For a regular shaped pool, multiply the length by the width by the depth.

How long after chlorine dosing will it take for chlorine levels to reach the lower chlorine limit and be deemed OK? 

This will vary a lot depending on how low the chlorine has fallen below the lower chlorine level, the amount of stabiliser in the pool and the type of dosage chemical used. Pool Gem has a time-out feature which will alert users of low chlorine levels, if from one hour after dosing, levels are still below the lower limit.

What is the acceptable pH and chlorine limits to set?

Pool Gem has factory set limits for pH of 7.2-7.8 and chlorine 1-5ppm. However, if unsure seek professional advice. Water monitoring may be slightly different for salt water pools as they operate just outside these limits.

In the chlorine box an “overrange” message appears. What does this mean?

The chlorine reading is greater than 5ppm. Pool Gem is not designed for the water monitoring of chlorine levels above this level. This will disappear once chlorine levels fall below 5ppm.

Will the Pool Gem chlorine and pH readings differ from results using alternative conventional water monitoring test methods?

There might be some discrepancy in the chlorine readings, if there are high levels of cyanuric acid in the pool (>50 ppm). The pH readings should be close to conventional water monitoring test results.

Can Pool Gem be used in a salt water pool?

Yes, Pool Gem can be used in salt water pools. However, the phosphate sensor will not work in salt water. In addition, no dosing information will be provided.

Can Pool Gem be used in non-chlorine sanitised pools?

No, as this requires different methods of water monitoring.

How does Pool Gem wireless communication work?

Pool Gem uses a Telegesis Zigbee radio frequency module (RF) in both the floating and receiver units. Every 15 minutes the RF module in the floating unit will wake up and transmit a signal at a frequency of 2.4GHz to the receiver unit. The signal contains the readings from the pool. The receiver displays the water quality reading. The RF module will then go back to sleep. The receiver will only receive the signal if it “recognises” the transmitters’ unique id number. Therefore, the floating unit and receiver are linked up prior to sale.

How does Pool Gem power itself?

Inside the floating unit are three rechargeable batteries. The batteries are constantly charged by a solar cell. The batteries do not need to be changed.  The receiver is powered by mains.

Can Pool Gem be used for indoor Pools?

Pool Gem can be used in a naturally well lit, indoor pool. However, extended periods of indoor use could flatten the batteries. If using indoors it is a good idea, every so often to take outdoors and charge up for a day or so for accurate water monitoring. It is not recommended to use Pool Gem in poorly lit indoor pools.

How do I insert the probe into the floating unit?

The instruction manual will provide full details on how to fit the probe to the floating unit. To tighten the probe, turn the loose collar at the top of the probe clockwise until finger tight.  DO NOT TURN THE WHOLE PROBE.

Can Pool Gem be used in above-ground Pools?


Will the app provide dosing information?

No, only the receiver will provide dosing information and only the receiver will allow you to preset limits. The app will just display readings and log data of the water monitoring.

Where do I download the App?

Free from the iTunes store

or via Google play for Android

From how many previous days will pool data be preserved?

The graphs will preserve data going back about 4 days.

What is the maximum distance that the receiver can be located way from the floating unit?

In an ideal environment, with straight line of sight and no obstructions, the maximum distance will be about 50 meters. However, there are a number of factors that could reduce this distance quite considerably, such as walls and wet foliage located between the floating unit and receiver. For maximum transmission distance it is advisable to float the unit away from the pool walls and to place the receiver in straight line of sight to the floating unit with minimal obstructions between the two.

If my neighbour has a Pool Gem will they not interfere with each other?

No. Each floating unit and receiver set is paired together in a secure network. No water monitoring data from a neighbour’s pool will interfere with your own data.

Will Pool Gem Interfere with other electronic devices within the house?


Can Pool Gem be used in a Spa or Hot tub?

It is possible, but not advisable. Pool Gem is not designed to measure bromine spas, and spas and hot tubs tend to be covered when not being used, which could cause battery recharge problems. In addition spas tend to operate with sanitiser concentrations outside those for which Pool Gem was designed for.

How do I tell that the probe needs changing?

The pH readings may differ widely from results from a conventional test method (>0.5 pH units) and/or the pH response change becomes very slow and sluggish.

Should I remove Pool Gem from the pool during bad weather (high winds and rain)?


Should Pool Gem be totally immersed under water?

NO. Pool Gem is designed to float in water and should not be fully immersed in water for a prolonged length of time. No data will be transmitted if Pool Gem is fully immersed.

Can Pool Gem be tethered to the side of the pool?


Should the unit be removed from the pool, if there are many users in the pool?

It is advisable to remove the unit when the pool is in use, especially with high bather load as this also affects the water monitoring process.