Comparison

Spa Calc vs the HTH App for Hot Tubs

The HTH app is mainly a pool app that also covers HTH spa strips through a color-matching chart, and its latest version notes announce new spa water testing. It recommends HTH products and saves history with a myHTH account. Spa Calc is made only for hot tubs, works with any kit and brand, and has no account.

Prices, features and ratings checked on 28 October 2026.
App Store rating as shown on 28 October 2026: 4.7 stars from 4.1K ratings on the US App Store (pool and spa app).

The short answer

The HTH app is a free, well-rated pool app that also handles HTH spa strips. Spa Calc is for people who want an app that only thinks about hot tubs: ready-to-soak, teaspoon doses for any brand, bromine and a drain countdown, with no account.

At a glance

From each app's own App Store page and website, checked on 28 October 2026. "Not listed" means we found no mention of it there, not that the feature is missing.
Feature	Spa Calc	HTH Pools App
Price	Free for one tub	Free
Made for	Hot tubs only	Pools, with spa strip testing
Strip testing	Enter values from any kit	Yes HTH spa strips via matching chart
Product recommendations	Generic chemicals at any strength	Yes HTH products
Doses in teaspoons for your products	Yes	Not listed
"Ready to soak?" check	Yes	Not listed
Bromine	Yes	Not listed
Dichlor then bleach tracker	Yes	Not listed
MPS shock with wait timer	Yes	Not listed
Drain and refill countdown	Yes	Not listed
Inflatable presets	Yes	Not listed
Test history	Yes No account needed	Yes With a myHTH account
Charts	Yes	Not listed
How-to videos and store locator	No	Yes
Account to sign up for	None	myHTH account to save history
Rental and service tools	Yes Plus and Pro	Not listed

Pricing

Our app

Spa Calc

Free$0Every feature for one tub, inflatables included.
Plus$1.99 a month, $14.99 a year or $39.99 onceUp to 10 tubs plus the host and pro tools. 1-week free trial on the yearly plan.
Pro$9.99 a month or $79.99 a yearUnlimited tubs plus the host and pro tools. 1-month free trial on the yearly plan.

Prices on the App Store at launch. Pricing is per person, not per tub.

Brand strip app with spa testing

HTH Pools App

HTH appFreeHTH spa strips through an interactive matching chart, product recommendations, history with a myHTH account. Version 5.4.10 notes: "New Universal Spa Water Testing".

Free on the App Store.

Prices as listed on 28 October 2026. Source

Both are free for one tub. HTH's app supports the HTH strips and products you buy. Spa Calc is paid only for more than one tub.

Built for the tub

Every screen in Spa Calc is about a hot tub: the soak check, the post-soak top-up, bromine, dichlor and bleach, filter rinses and drain day. Doses are sized for a few hundred gallons, in teaspoons down to an eighth.

Any brand, any kit

Spa Calc doesn't recommend a brand. Add the products you own at the strength on their labels and every dose is worked out for them. Use whatever strips or drop kit you like.

No account

Your tub, tests and doses stay on your phone and back up to your own iCloud. Nothing to sign up for, and no personal details asked.

What HTH App Users Complain About

Paraphrased from public reviews. Each one links to where it was posted and gives the month it was written.

Spa mode hard to use. In January 2024 a reviewer said spa mode had no scanning and the color boxes ran off the screen, so they couldn't pick the right colors (App Store review, January 2024). HTH's newest version notes announce new spa water testing, so this may have changed.

Spa Calc approach: entry is a number pad on one screen, with steps that match your kit.
Personal details before testing. A July 2024 reviewer said scanning asked for "a lot of personal info like name, address" (App Store review, July 2024).

Spa Calc approach: no account and no personal details.
Different results from the same strip. A July 2025 reviewer said ten photos of one strip gave different results (App Store review, July 2025).

Spa Calc approach: no photo reading; the numbers are the ones you read.

When HTH is the better choice

You use HTH strips and products and want the app to match them.
You have a pool and a hot tub and want both in one free app.
You want how-to videos and a store locator.

Questions people ask

Is there an HTH app for hot tubs?

Yes. The HTH Pools App covers HTH spa strips through a matching chart, and its version 5.4.10 notes announce new universal spa water testing (App Store, 28 October 2026). Spa Calc is a separate app made only for hot tubs.

Do I need HTH strips to use Spa Calc?

No. Spa Calc takes values from any strip or drop kit; you read the strip against its own chart and enter the numbers.

Which hot tub app works without an account?

Spa Calc has no account at all. The HTH app presents a myHTH account as the way to save your history.

More comparisons

All comparisons

References

HTH, Test to Swim, HTH spa and myHTH are trademarks of their respective owners. Spa Calc is not affiliated with them. Information checked on 28 October 2026; prices and features change. Corrections: [email protected]