Not sure what number to set? This page is your cheat sheet. For every reading, here's the ideal range and the thresholds other pros actually alert on, with the reason each one matters. Pair it with How to Set Up Alerts: pick your number here, flip the switch there.

You don't need all of them. Skim the list, find the ones that solve a headache you have today, and turn those on first.

One rule that holds across all of them: set your threshold outside your normal range, not at the edge of it. The alert should fire where you'd want a phone call, not where the water is slightly off.

If you alert too tight, you'll drown in pings and turn the feature off.

Free Chlorine Alerts

Ideal range: 2 to 4 ppm

Below 2.0 ppm: Early warning before it hits zero on a hot week.
Below 1.0 ppm: Sanitizer is failing. Algae and green-pool risk. This is the big one.
Below 0.5 ppm: Emergency. The pool is effectively unsanitized.
Above 5.0 ppm: Overdosing and wasting product.
Above 8.0 ppm: Too high to swim. Comfort and liner concern.
Above 10.0 ppm: Likely a data-entry error or major overdose. Worth a look.

In practice, pros set their low alert anywhere from below 1 to below 3 ppm, and their high alert from above 5 to above 8, depending on how tight they run their water. Pick the number where you'd want a phone call.

pH Alerts

Ideal range: 7.4 to 7.6

Below 7.2: Corrosive water that eats plaster and equipment.
Below 7.0: Aggressive. Real risk to surfaces and metal.
Below 6.8: Severe. Likely a feeder or dosing problem.
Above 7.8: Chlorine effectiveness drops and scaling starts.
Above 8.0: Cloudy water, chlorine barely working.
Above 8.2: Far out of range. Scaling and customer complaints likely.

Common real-world picks: a high alert around 7.8 to 8.0, a low alert around 7.0 to 7.4.

Total Alkalinity Alerts

Ideal range: 80 to 120 ppm

Below 60 ppm: pH starts bouncing and is hard to hold stable.
Below 50 ppm: No buffer left. pH will swing daily.
Below 40 ppm: Severe. Expect corrosive conditions.
Above 140 ppm: pH locks high and scaling begins.
Above 180 ppm: Heavy scaling risk and hard to lower pH.
Above 200 ppm: Way out. Likely a fill-water or dosing issue.

Common picks land near above 150 / below 60 to 70

Cyanuric Acid Alerts

Ideal range: 30 to 50 ppm

Below 20 ppm: Chlorine burns off in the sun. Chasing chlorine all summer.
Below 10 ppm: Almost no UV protection. Huge chlorine waste.
Above 80 ppm: Chlorine lock starting. Sanitizer choked.
Above 100 ppm: Chlorine effectively blocked. Drain needed.
Above 150 ppm: Severe. Explains a high-cost pool instantly.

Pros commonly alert low around 30 to 50, and high anywhere from above 70 to above 90. The wide spread reflects how differently salt and chlorine pools tolerate CYA.

Calcium Hardness Alerts

Ideal range: 200 to 400 ppm

Below 150 ppm: Aggressive water pulls calcium from plaster and grout.
Below 100 ppm: Severe corrosion risk to surfaces.
Above 450 ppm: Scaling on surfaces and equipment.
Above 600 ppm: Heavy scale, cloudy water, equipment risk.
Above 800 ppm: Extreme. Fill-water or evaporation problem.

Salt / Salt Cell Alerts

Ideal range: 3000 to 3900 ppm

Below 3000 ppm: Early nudge before the generator struggles.
Below 2700 ppm: Generator underproduces chlorine.
Below 2400 ppm: Cell may stop producing entirely.
Above 4500 ppm: Risk to the cell and possible corrosion.
Above 5000 ppm: Too high. May need to dilute.

Salt cell output departure above 80%: the cell is working much harder than baseline to hit the same chlorine, an early sign it's aging or scaling.

Salt / TDS above 3600 ppm: total dissolved solids climbing, which can shorten cell life.

Swing-Based Alerts

These watch for a big jump between visits instead of a fixed number. They catch leaks and equipment failures a static high or low would miss.

Free Chlorine dropped by 50% or more since last visit: an early-warning catch for algae blooms before they're visible. A percentage swing catches a pool trending the wrong way even when the absolute number still looks okay.
Free Chlorine dropped more than 3 ppm since last visit (use the "changed by too much" alert): Possible leak, heavy bather load, or feeder failure.
pH jumped more than 0.6 since last visit (use the "changed by too much" alert): Feeder malfunction, fresh fill, or dosing error.
Tabs jumped well above this pool's recent average: something changed at that property, or the tech is over-correcting.
Shock usage spiked over the prior few visits: a pool trending the wrong way, caught before it turns green.

Tab Alerts

Higher than 3 tabs per visit: a tech is loading more chlorine than your standard. Wasted product and shrinking margin. Set this to whatever your own per-visit cap is.
Higher than 5 tabs per visit: well past any normal load. Either a real demand issue at that pool or a dosing habit worth a conversation.
Lower than 1 tab per visit: a pool getting almost no chlorine feed. Quality risk, or a tech skipping the feeder.

Shock Alerts

Higher than 2 lbs per visit: more shock than a routine stop should need. Flags a struggling pool or a heavy hand.
Higher than 5 lbs per visit: a big correction. Worth knowing whether it was justified and whether it should have been billed.

Additional Dosage Caps We See

Liquid Chlorine above ~4.5 gal per visit
Cal-Hypo above ~1 lb per visit (catches overdosing)
Muriatic Acid above ~1 gal per visit
Cal-Hypo shock increased by ~50 lbs (a big jump worth a look)

Other Alerts Worth Knowing About

The thresholds above are the fully customizable ones, where you pick the reading, the condition, and the number. Skimmer has a second set of alerts that simply turn on or off and notify you by panel or email when something happens (no threshold to set). These cover operational moments like a stop getting skipped, a payment failing, AutoPay turning off, or a work order finishing.

They aren't as customizable, but they're just as useful. See the Starter Guide to Skimmer Alerts & Issues for ready-made packs that mix these in.

Alert Inspiration: Thresholds Worth Considering