pH · E.W.A. watches this
7.2 to 7.6
How acidic or basic the water is. Below 7.2 the water stings and eats your heater. Above 7.6 the sanitizer stops working and scale builds up.
Water balance 101
Spa and pool water, explained in plain words.
Four numbers decide whether your water is safe, comfortable and cheap to keep. Here is what each one means, the range to hold it in, and exactly what to add when it drifts.
The four numbers that matter
E.W.A. watches the first three around the clock. The fourth you set once and check now and then, it is the buffer that holds the rest steady.
Sanitizer · E.W.A. watches this
650 to 750 mV ORP
How strongly the water actually kills bacteria, measured as ORP. A number in ppm can look fine while the water is unsafe. ORP reads the real killing power.
Temperature · E.W.A. watches this
Steady
Comfort, running cost and sanitizer speed all ride on temperature. A sudden drift is an early sign of a heater or flow problem.
Total alkalinity
80 to 150 ppm
The buffer that keeps pH from swinging. Set it right once and pH stays put. This one you set and check occasionally, it does not move fast.
pH, the one to fix first
pH is how acidic or basic the water is, on a scale where 7 is neutral. For a spa or pool you want it between 7.2 and 7.6. It sounds like a narrow window because it is, and it matters more than any other number.
When pH drops too low, the water turns acidic. It stings eyes and skin, and it slowly corrodes your heater, pump seals and any metal it touches. When pH climbs too high, two things happen at once: your sanitizer stops doing its job, and calcium starts to fall out of the water as white scale on the waterline and inside the plumbing.
The fix is simple once you know which way it went. Too low, add a pH increaser. Too high, add a pH decreaser. The hard part has always been reading it accurately, which is where a paper strip lets you down.
Sanitizer, and why ORP beats ppm
Sanitizer is what kills bacteria before it reaches you, usually chlorine or bromine. Most people measure it in parts per million (ppm), the amount of sanitizer in the water. The problem is that a normal ppm reading can hide unsafe water, because how well sanitizer works depends heavily on pH.
That is why E.W.A. reads ORP (oxidation reduction potential), measured in millivolts. ORP is the real killing power of the water, not just how much sanitizer is floating in it. Hold it between 650 and 750 mV and the water is genuinely safe. Let it fall and bacteria and algae take over, which is when a spa turns green.
When sanitizer runs low, you shock the water, a large dose that resets it, then hold it in range. If it keeps disappearing, the cause is usually high demand, high pH, or too little stabilizer.
Alkalinity, the buffer behind pH
Total alkalinity is the water's resistance to pH change. Keep it between 80 and 150 ppm and your pH stays where you put it. Let it drift and pH starts bouncing, high one day, low the next, no matter how much you dose. Set alkalinity correctly first, and pH becomes easy to hold. This is the one number you can check with a strip now and then, it does not move quickly.
Temperature, comfort and cost
Temperature is not a chemical, but it drives three things: how the water feels, how much it costs to keep warm, and how fast your sanitizer is used up. A steady temperature is efficient and safe. A sudden drift is an early warning of a heater or flow problem, which is why E.W.A. watches it alongside the chemistry.
Read the water: symptom to fix
The water tells you what is wrong before a test does. Here is how to read it.
| What you see | Likely cause | What to do |
|---|---|---|
| Cloudy, milky water | pH or alkalinity out of range, or weak sanitizer | Check pH first, then shock the sanitizer |
| Green, slimy water | Sanitizer too low, algae took hold | Shock hard, then hold sanitizer in range |
| Stinging eyes, harsh smell | pH too low, or combined chlorine (chloramines) | Raise pH, then shock to burn off chloramines |
| White scale on the waterline | pH or alkalinity too high, hard water | Lower pH and alkalinity, keep them in range |
| Sanitizer disappears fast | High demand, low stabilizer, or high pH | Shock, check pH, add stabilizer if needed |
These are general starting points, not a prescription. Your exact dose depends on water volume and how far off the number is. E.W.A. reads your water and tells you the specific amount to add.
Why a paper strip cannot do this
A strip gives you a colour and a shrug. You hold it against a printed chart and guess which block it matches, and the honest truth is that two people read the same strip as two different numbers. By the time the water looks wrong, it has been wrong for a while.
E.W.A. reads pH, sanitizer and temperature every ten minutes, the same way every time, and tells you in plain words exactly what to add. No squinting at colours, no guessing. That is the whole idea: perfect water, without the guesswork.
Common questions
What is the single most important number?
pH. It decides whether the water is comfortable and whether your sanitizer even works. Get pH right first, then everything else is easier to hold.
Why measure ORP instead of chlorine in ppm?
ppm tells you how much sanitizer is present. ORP tells you how well it is actually working. Water can show a normal ppm and still be unsafe if the pH is off. ORP reads the real killing power, which is what keeps you safe.
How often should I test?
By hand, most owners test a few times a week and miss the drift in between. E.W.A. reads pH, sanitizer and temperature around the clock, so you see a problem on hour one, not when the water is already green.
Do I still need test strips?
Strips give a rough colour and a guess, and two people read the same strip differently. Use a strip now and then for alkalinity and hardness, and let E.W.A. watch the numbers that move fast.
What do I actually add when a number is off?
Low pH, add a pH increaser. High pH, add a pH decreaser. Weak sanitizer, shock the water. E.W.A. names the problem in plain words so you are not guessing which bottle to reach for.
Does this work for pools too?
Yes. The same four numbers balance a pool. E.W.A. reads the water itself, not your equipment, so it works on any spa and any pool.
Stop guessing at your water.
E.W.A. reads pH, sanitizer and temperature in real time and tells you exactly what to add. Simply perfect water, every time.