When we reviewed the original Crystal Water Monitor, it earned high marks for its ease of use and accurate readings. The 2025 Crystal Water Monitor reviewed here is just as easy to use and comes with an upgraded sensor that is even more accurate and offers a longer lifespan than the original. This monitor is not cheap, starting at $449, and you’ll have to pay an annual $99 fee to take full advantage of all of its app and cloud features, but that fee also provides a full warranty on all parts, including the sensor. Perfectly balanced water, continuous monitoring, and historical water chemistry reports make the Crystal Water Monitor our Editors' Choice winner for smart pool monitors.

Design: A Discreet Puck

The latest Crystal Water Monitor looks exactly like the original version. The white puck-shaped monitor measures 2.0 by 5.5 inches (HW) and has a textured magnetic lid. Beneath the lid is a waterproof compartment for three AA batteries (included) that will last up to a year before requiring replacement. In this compartment is also a button for resetting the device and taking an on-demand water sample, and an LED light that flashes white while the monitor is in setup mode, flashes blue during an on-demand test, pulses green after a successful setup or on-demand measurement, and blinks red if there's an issue with the device.

Crystal offers two versions of the Water Monitor: one for bromide and chlorine ($449) and another for salt water ($479).

(Credit: Crystal)

The monitor, which is placed outside of the pool or spa, uses a 2.4GHz Wi-Fi radio to connect to your home network and the Crystal Water Monitor mobile app (available for Android and iOS). It utilizes a gel-based waterproof sensor, which is 7 inches long and is attached to a 43-inch cable that plugs into a port on the side of the monitor. The sensor sits in the water at a depth of around 18 inches. The original Crystal Monitor sensor had a life expectancy of two years before needing to be replaced, but the new one should last more than three years.

According to a company spokesperson, the new sensor also delivers more accurate readings. The monitor takes 144 water quality readings per day (one every 10 minutes), including the ORP (Oxidation Reduction Potential) level, a measure of the water’s sanitizing potential, directly related to the amount of free chlorine in the water. It also measures the pH (acidity) level and the water temperature.

The monitor comes with a test strip kit that lets you manually check your water’s Free and Total Chlorine levels as well as its alkaline, hardness, and cyanuric acid levels. You can enter these values into the app and receive chemical dosage advice to bring each measurement to an acceptable level. Also included with the Crystal Water Monitor are mounting brackets, screws, adhesive, and plastic ties for attaching the monitor to a pool ladder or the side of a hot tub.

While the Crystal Water Monitor is very easy to use and will tell you everything you need to know to keep your water chemistry perfectly balanced, you’ll have to pay $99 per year to connect to the cloud service and receive chemical dosage advice (the first year is free). The subscription also provides historical water quality readings, the ability to enter test strip values into the app, and the peace of mind you get with a replacement warranty for all parts for as long as you remain a subscriber. That means that when your sensor reaches its end of life, the company will send you a new one free of charge.

While Crystal’s $449 or $479 up-front price and $99 per year subscription may seem steep, it's actually more cost-effective than many other pool water monitors. The WaterGuru Sense S2 has an initial cost of $388, but requires a new cassette every month. It comes with one cassette, but additional cassettes go for $69 for a pack of three, so if you keep your pool open for six to seven months of the year, you’ll pay $536 for the first year and an additional $138 every year thereafter. The Sutro Smart Water Monitor has an initial cost of $499 and also requires a new cartridge every month. With a Basic subscription, you get on-demand cartridge replacements, but it’ll cost you $29 per month, which means you’ll have to pay an additional $180 per year if you keep your pool open for half the year.

(Credit: Crystal)

The Crystal Water Monitor mobile app hasn’t changed since the last generation, and that’s a good thing. The device appears on the home screen, where it is represented by a large icon in the shape of the monitor. The icon appears blue when the water is balanced and turns orange if the water chemistry is off. The icon displays the name of the monitor, the current water temperature, the time since the last reading, and the number of actions needed (if any).

When you tap the icon, it opens a screen with the temperature, the latest pH, ORP, and temperature readings, and historical charts for all three readings (day, week, month, three months, and year). Here you can also submit a manual water report using the included test strips. Simply dip a strip in the water, tap the plus button, and use your phone's camera to take a snapshot of the strip. You can also enter the reading values manually. Once the results are sent to the cloud, you’ll receive recommendations for chemical doses to correct any problems.

Tap the gear icon in the upper right corner to access the settings screen, where you can view and edit general information such as the name of your pool or spa, water volume, and sanitizer protocol (chlorine, bromine, salt). You can also enter the type of chemicals you use (which dictates what dosage advice you’ll receive), add drain and refill dates, view recent actions, and update your subscription.

Installation and Performance: Swift to Set Up, and Easy to Use

Setting up the Crystal Monitor is easy. I downloaded the mobile app, created an account, and tapped Setup on the monitor tab. I installed the batteries, plugged in the sensor, and used a Philips screwdriver to attach the pole mount to the monitor. I then attached the monitor to my ladder pole using the included zip ties. I scanned the QR code on the battery compartment when prompted, selected my Wi-Fi SSID from the list, and entered my Wi-Fi password, at which point the monitor immediately connected to the cloud. I tapped Next and scanned the QR code on the monitor when prompted, then removed the cap (you’ll want to save the cap for winter storage) and placed the sensor in the pool at a depth of around 18 inches. After 40 minutes, I received my first reading.

(Credit: John R. Delaney)

The Crystal Water Monitor worked perfectly in my tests. When I received my first reading, it told me that my pH and total alkalinity levels were low and suggested I add 9 pounds of baking soda to the water, which I did. After an hour or so, my pH reading came back at 7.6 parts per million (ppm), and my total alkalinity was at 90ppm, both of which are ideal for my pool. After two very hot and sunny days, I received an alert that action was needed, so I opened the app and saw that my ORP levels were low. Following the app’s advice, I added slow tabs to my chlorinator and within an hour, my ORP levels were where they should be.

The monitor’s measurements were very accurate, matching the measurements I received from digital pH and ORP meters and from manual test strips. Water temperature readings were in line with a pool thermometer placed in the same area, and push notifications arrived quickly.