ICO Spa Water Monitor | Pool Express

Name: ICO Spa Water Monitor
Brand: Ondilo
SKU: ICO-SPA
Price: 449 USD
Availability: OutOfStock

$449

Sold out

Why it stands outICO Spa floats in your hot tub and measures temperature, pH and sanitizer level (ORP) every hour, with TDS or salt on the saltwater version, then sends dosing advice sized to your spa to your phone over Wi-Fi. Rated for water up to 104°F, with no subscription.

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Measures temperature, pH and sanitizer level (ORP) every hour; TDS or salt on the saltwater version
Rated for spa water from 50°F to 104°F (10–40°C)
Works with chlorine, bromine and saltwater spas; no subscription

ICO Spa

Water quality monitoring in the palm of your hand. The ICO you know, configured for the hot tub.

ICO Spa monitor with the ICO app on a phone

Does ICO work for spas? Yes.

Yes. ICO Spa is the version of Ondilo's ICO monitor configured for hot tubs and spas: the same floating device and the same ICO app as ICO Pool, delivered with spa probes and spa-specific advice. It floats in the spa or sits in the skimmer under the flap, keeps working with the cover closed as long as the Wi-Fi signal gets through, and measures the water once an hour.

Always on. Always watching.

ICO tracks your spa water around the clock: temperature, pH and sanitizer level every hour, with TDS or salt on the saltwater version.

Intelligence that anticipates

The app reads the trend, predicts what the water needs and sends dosing advice sized to your spa straight to your phone.

Connected. Everywhere.

Direct Wi-Fi to your router, so you check the spa from the couch or from another state. No gateway, no subscription.

Extraordinary in every way.

ICO Spa merges hourly sensing with artificial intelligence to evaluate your water continuously. The system learns your spa and keeps the water right with minimal effort from you.

Freedom you can feel

Conventional spa care means strip tests, chemical runs and service appointments. ICO Spa removes most of them: its sensors and the ICO algorithms watch the chemistry and tell you exactly what to add, so the guesswork goes and the water stays ready.

Commercial quality. Personal scale.

The ORP (sanitizer effectiveness) measurement that commercial facilities rely on, in a monitor that floats in a home hot tub. Professional standards without the professional price.

Less cost. More joy.

A spa should not drain your time or your wallet. Ondilo reports chemical savings of up to 50% and 80% less maintenance time for ICO owners, because you add what the water needs rather than what the bottle says.

Simplicity that delights

From the box to running in minutes: place ICO Spa in the water, connect it to the app and let it work. No technician, no complex setup, no recurring fees, and a monitor that gets smarter the longer it floats.

The intelligent Water Index

Patented technology for pristine spa water

The ICO Water Index sums up your spa's quality, balance and comfort in one color. Its AI weighs past, present and projected readings, with the local weather, and turns them into instant insight and maintenance suggestions before the water drifts.

ICO Water Index colors from clear blue to red

Setting up ICO Spa in a hot tub

Connect it to Wi-Fi

Open the ICO app, add ICO Spa and join your 2.4 GHz network. Set up the spa profile: volume, treatment (chlorine, bromine or salt), the products you use and your preferred ranges.

Float it, or park it in the skimmer

Drop ICO Spa in the water or set it in the skimmer under the flap; it keeps working with the cover closed. Leave it in for 24 hours, then calibrate the probes with the included kit.

Read the hourly results

Every hour the app shows temperature, pH and ORP (plus TDS or salt on the saltwater version), the Water Index color and what, if anything, to add. Alerts arrive on your phone before the water turns.

Maintenance: what a season looks like

Each season. Calibrate the pH and ORP probes with the ICO calibration kit (at least every six months) and top up the charge; one charge lasts six months or more.

After a drain and refill. Small spas are drained a few times a year. Put ICO back in once the new water has circulated, update the treatment in the app if it changed, and let a day of readings settle before trusting the trend.

Winter and storage. If the spa is shut down, switch on the wintering mode in the app when the monitor is out of the water for more than 24 hours, wipe it, air-dry it for 12 hours, charge it to at least 80%, store it indoors (59–77°F) and keep the probe caps moist in KCl solution; never in demineralised water.

Personalized. Precise. Perfect.

The ICO app turns the hourly readings into recommendations sized to your spa: how much of which product to add and when, alerts before a problem shows, and a Water Index color score that says at a glance whether the water is ready.

Proactive maintenance notifications
Chemical doses sized to your spa's volume
Climate-aware care through the seasons
Filtration efficiency recommendations
Long-term history of every reading

ICO Spa measures and advises only; it does not dose chemicals, so you still add what the app recommends.

Beautifully small.
Incredibly powerful.

ICO Spa monitor next to apples for scale

Engineered for simplicity

Reinforced polymer housing and overmolded probes on a twist-lock mount, with the installation tool in the box. A worn probe is swapped in a minute.

Designed to perform

IP68 waterproof, about 5.9 in tall and 4.3 in across (15 by 11 cm); fits in the skimmer under the flap, and it keeps measuring with the spa cover closed.

Effortlessly connected

Links directly to your home router over 2.4 GHz Wi-Fi (802.11 b/g/n, WPA/WPA2) plus Bluetooth Low Energy for setup. A Wi-Fi extender or powerline adapter (not included) carries the signal to a spa far from the house, and a closed cover can weaken it. During an outage the monitor stores up to 42 hours of readings and sends them when the connection returns.

Power that lasts

Rechargeable battery rated for more than 3,000 cycles; one charge lasts six months or more, so most owners charge once a season. Charge with the included USB cable from a 5 V, 1–3 A charger, out of the water and after the unit has dried for 12 hours; never longer than 12 hours.

An app as calm as your spa

The ICO app shows every vital parameter on one dashboard, with live readings and trend graphs, so a glance tells you whether the water is ready.

Water quality, visualized

The Water Index turns the chemistry into one color.

Clear blue: excellent water, nothing to do
Deep blue: good water, a minor adjustment may help
Orange: quality is slipping, act on the advice
Red: alert, stay out until it is corrected
Grey: not enough readings yet

Monitoring that never sleeps

Every hour, day and night: temperature, pH, sanitizer effectiveness (ORP) and, on the saltwater version, dissolved solids or salt. No strips, no guessing.

Temperature
pH
Sanitization (ORP)
TDS / salt on the saltwater version

Tailored to your spa

Set the spa's volume, your treatment, the products you keep and your preferred ranges, and the advice is sized to that water, not to a pool.

The AI weighs the history, the current readings and the forecast, with the local weather, to keep the balance.

Share the readings

Share ICO's latest readings and advice with the household, a guest or your service technician in a tap; they can update you just as quickly.

Pricing, accessories and ongoing fees

What ICO Spa costs to own, in full. There is no subscription and nothing to buy monthly; the recurring item is the seasonal calibration kit.

ICO Spa pricing and ongoing costs
Item	Cost	How often
ICO Spa monitor	$449 list price · sold out at Pool Express	Once; 2-year manufacturer's warranty
ICO app	Free, every feature	No subscription or premium tier
Calibration kit	About $49	Each season (at least every 6 months); the same kit as ICO Pool
Replacement pH or ORP probe	About $149 each	After several seasons, one probe at a time
KCl storage solution	Sold by Ondilo	For storing the probes over the winter
Wi-Fi extender	Not included	Only if the router's signal does not reach the spa

ICO Spa vs. WaterGuru SENSE S3 and Sutro

The two monitors hot-tub owners most often ask about alongside ICO. WaterGuru is built around a pool skimmer and a daily cassette test; Sutro's service has ended.

ICO Spa compared with WaterGuru SENSE S3 and Sutro
Feature	ICO Spa This page	WaterGuru SENSE S3	Sutro
Made for	Hot tubs and spas (and ICO Pool for pools)	Pool skimmer	Pools and spas (service ended)
Readings	Every hour, 24 a day	One cassette test a day	None: the app and cloud service ended October 31, 2025
What it measures	pH, ORP, temperature; TDS or salt on the saltwater version	Free chlorine, pH; alkalinity, CYA and hardness with the C5+ cassette	pH, free chlorine, alkalinity (historical)
Ongoing cost	About $49 calibration kit a season; no app fee	C5+ cassettes, about $289 a year at one test a day	Was a monthly cartridge subscription
Water temperature rating	50–104°F (10–40°C)	Not published for hot tubs; ask WaterGuru before using one in a spa	Not applicable
Power	Rechargeable, 6+ months per charge	Solar with USB-C backup	Rechargeable (historical)
Connection	Direct 2.4 GHz Wi-Fi + Bluetooth	Direct Wi-Fi	Wi-Fi hub (historical)
Bottom line	The one spa monitor here with hourly readings and no consumables	A good pool test kit on a timer; not sold as a spa monitor	Do not buy: old stock cannot give readings

Competitor figures are the makers' published ones as collected for our best pool water monitors guide; see ICO vs WaterGuru and ICO vs Sutro for the full comparisons.

Spa care, redefined.

ICO Spa blends commercial-grade monitoring with AI-driven insight to keep hot-tub water clear, balanced and safe without the chore of testing it.

Have a swimming pool as well? ICO Pool is the same monitor configured for pools, in chlorine/bromine and saltwater versions, and it is in stock.

Spa fit, temperature limits and upkeep

Does ICO work in a spa?

Temperature
pH
Sanitization (ORP)
TDS / salt on the saltwater version

Not for: Spas treated with active oxygen. Copper-based treatments can also block the readings.

What you still do: ICO Spa measures and advises only; it does not dose chemicals, so you still add what the app recommends.

Temperature, power and upkeep

Water temperature: Rated for water from 50°F to 104°F (10–40°C), which covers a hot tub set at the usual 100–104°F. Prolonged use below 59°F (15°C) can shorten battery life.
Connectivity: Links directly to your home router over 2.4 GHz Wi-Fi (802.11 b/g/n, WPA/WPA2) plus Bluetooth Low Energy for setup. A Wi-Fi extender or powerline adapter (not included) carries the signal to a spa far from the house, and a closed cover can weaken it. During an outage the monitor stores up to 42 hours of readings and sends them when the connection returns.
Battery: Rechargeable battery rated for more than 3,000 cycles; one charge lasts six months or more, so most owners charge once a season. Charge with the included USB cable from a 5 V, 1–3 A charger, out of the water and after the unit has dried for 12 hours; never longer than 12 hours.
Calibration: At least every six months, or after a long time out of the water. The ICO calibration kit is the same for ICO Pool and ICO Spa and sells for about $49.
Consumables: A calibration kit each season; pH and ORP probes are overmolded, twist-lock parts replaced individually when they wear out (about $149 each), and are stored in KCl solution over the winter. No cassettes, strips or app fees.
Size: About 5.9 in tall and 4.3 in across (15 by 11 cm); fits in the skimmer under the flap
App: Free ICO app for iPhone and Android; works with Alexa, Home Assistant, Jeedom and eedomus.
Subscription: No subscription, premium app tier or hidden fees.

ICO Spa vs. ICO Pool: what is different

ICO Spa compared with ICO Pool
Feature	ICO Spa This page	ICO Pool
Designed for	Hot tubs and spas	Swimming pools
Device and app	Identical hardware and app	Identical hardware and app
What you get	Spa probes (pH and ORP; TDS on the saltwater version) and a spa color	Pool probes (pH and ORP; TDS on the saltwater version) and a pool color
Advice and alerts	Dosing by spa volume; spa-specific notifications through the year	Dosing by pool volume; pool-specific notifications such as winterizing advice
Treatments	Chlorine, bromine, salt (not active oxygen)	Chlorine, bromine, salt
Water temperature	50–104°F (10–40°C)	50–104°F (10–40°C)
Readings	Every hour	Every hour
Battery	Rechargeable, 6+ months	Rechargeable, 6+ months
Warranty	2 years	2 years
Price	$449 · sold out at Pool Express	From $449 · in stock

Ondilo supplies each version with the probes and the advice that match where it goes, so choose by what it will float in. The calibration kit and the replacement probes are the same for both. See ICO Pool.

Specifications

ICO Spa Water Monitor specifications
Designed For	Hot tubs and spas
Measures	Temperature, pH, Sanitization (ORP), TDS / Salt on the Saltwater Version
Works With	Chlorine Spas, Bromine Spas, Saltwater Spas
Water Temperature	50–104°F (10–40°C)
Readings	Every hour, sent to the ICO app
Connectivity	2.4 GHz Wi-Fi and Bluetooth LE

ICO Spa Water Monitor specifications, continued
Battery	Rechargeable, 6+ months per charge, USB
Size	About 5.9 in tall and 4.3 in across (15 by 11 cm); fits in the skimmer under the flap
Subscription	None
Warranty	2-Year Manufacturer's Warranty
Brand	Ondilo
Model Number	ICO Spa

Manuals, warranty and returns

Warranty

2-Year Manufacturer's Warranty from Ondilo. Every product carries the manufacturer's warranty shown on its page. Pool Express is an authorized dealer, so your warranty is valid.

Returns

Try it in your pool for 30 days. If it is not right for you, return it within 30 days of delivery for a full refund of the purchase price. You pay the return shipping. There is never a restocking fee. Full return policy

Manuals and documents

The manual ships in the box. Need a digital copy? Contact us and we will send it.

Shipping

Free shipping on every order to the contiguous United States. Orders placed by 2:00 pm Central Time, Monday through Friday, ship the same business day. Orders placed later ship the next business day. Most orders arrive 1–3 business days after they ship. Allow up to 5 business days for rural addresses. Shipping details

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ICO Spa questions: foaming, high temperatures, small volumes

Does ICO work in a hot tub?

Yes. ICO Spa is the version Ondilo configures for spas: the same device and app as ICO Pool, with spa probes and spa-specific advice. It is rated for water from 50°F to 104°F, fits in the skimmer and keeps working under a closed cover when the Wi-Fi signal reaches it.

What is the difference between ICO Spa and ICO Pool?

The hardware, the app and the way they work are identical. They differ in color, in the probes supplied (ICO Spa comes with pH and ORP probes, plus TDS on the saltwater version) and in the notifications: the advice for a spa, including dosing by its small volume, is not the advice for a pool. Choose by what the monitor will float in.

How hot can the water be?

Ondilo rates ICO for water up to 104°F (40°C), the top of the range most hot tubs are set to. Keep the set point at or below 104°F. Long periods below 59°F shorten battery life, which only matters if the spa sits cold.

My spa foams. Will ICO warn me?

Foam comes from body oils, lotions, detergents and water that has carried a high load of dissolved solids for too long; ICO does not measure foam itself. What it does show is the pH and sanitizer (ORP) trend behind it, and on the saltwater version the TDS reading that climbs as the water loads up. When the app keeps asking for more sanitizer while ORP stays low, a drain and refill is usually the fix.

Do readings swing in a small spa?

They do. A few hundred gallons at 102°F reacts within minutes to bathers and to every scoop of chemicals, so a single strip test can mislead. Hourly readings show the swing and the recovery, and the app doses by the spa volume and the products you set up, so you add what that water needs rather than a pool-sized amount.

Does ICO Spa add chemicals for me?

No. ICO Spa measures and advises; you add what it recommends. It replaces the guesswork and most of the strip testing, not the chemicals.

Is there a subscription?

No. The full ICO app is free, with no premium tier or test cassettes. The only recurring cost is the calibration kit each season and, after a few years, a replacement probe.

When will ICO Spa be back in stock?

It is sold out at Pool Express right now. Chat with a Pool Pro to be told when it is back, or, for a swimming pool, ICO Pool is in stock in chlorine/bromine and saltwater versions.

Have a question about your spa? Ask a Pool Pro.

Why shop at Pool Express?

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Free shipping on every order to the contiguous United States. Estimated delivery: 1–5 business days after you order.

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Try it in your pool for 30 days. If it is not right for you, return it within 30 days of delivery for a full refund of the purchase price.

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Find an identical, in-stock item advertised for less by an authorized U.S. dealer and we match the price before you buy.

Pool Pros on the phone

Talk to our in-house pool professionals before and after the sale: 512-961-3881, Monday–Friday, 8:00 am–5:30 pm Central Time.