Domakihub How to Test and Adjust Spa Water the Right Way
Keep your hot tub or spa safe, clear, and comfortable with a simple weekly testing routine.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
A spa that looks clear is not always safe — imbalanced water can irritate skin, corrode jets, and cloud your tub within days. The video above walks through the chemistry fundamentals; the steps below translate that into a practical routine for homes, holiday villas, and hotel spas in Greece, where hard water and high summer temperatures put extra pressure on chemical balance. Follow this guide once a week and your spa stays guest-ready year-round.
Why Spa Water Needs More Attention Than a Pool
A spa holds far less water than a swimming pool — typically 1,000 to 2,000 litres — yet it operates at 36–40 °C and is used at high bather density. Heat accelerates chemical consumption, and body oils, sunscreen, and sweat overwhelm the water quickly. This means a spa needs testing at least twice a week in heavy use, not just monthly like a larger pool.
In Greece, tap and well water is often hard (high in calcium and magnesium). Hard water raises the risk of scale forming on heating elements and jets, which can cut equipment life dramatically. Testing for calcium hardness alongside the standard parameters is therefore essential here.
The Three Numbers That Matter Most
Three parameters govern virtually all spa water problems: pH (acidity), total alkalinity (TA), and sanitiser level (usually chlorine or bromine). pH should sit between 7.2 and 7.6. Total alkalinity, which acts as a buffer to stabilise pH, should be 80–120 ppm. Sanitiser (free chlorine) should read 3–5 ppm in a spa; bromine users target 3–6 ppm.
Calcium hardness (150–250 ppm) and cyanuric acid (0 ppm for indoor spas, 30–50 ppm for outdoor spas with a stabiliser programme) round out a complete picture. If you only ever test three things, make them pH, TA, and sanitiser — but run the full panel monthly.
How to Test and Adjust Your Spa Water: 5 Steps
- 1
Collect a water sample correctly
Turn on the jets for 30 seconds to circulate the water, then collect a sample from elbow depth (about 30 cm below the surface) — not from the surface or near a jet return. Use a clean plastic cup or the vial that came with your test kit. Taking the sample from the right depth gives you a representative reading of the bulk water, not a localised hotspot.
- 2
Run the full test
Dip a multi-parameter test strip into the sample for the time stated on the pack (usually 15 seconds), then hold it flat and compare to the colour chart immediately. For higher accuracy — especially before balancing after a water change or before a busy holiday period — use a liquid drop-test kit or a digital photometer. Record the results: pH, total alkalinity, free chlorine (or bromine), and calcium hardness.
- 3
Adjust total alkalinity first
Always correct total alkalinity before touching pH, because TA buffers pH and changes to TA shift pH as a side effect. If TA is low (below 80 ppm), add sodium bicarbonate (baking soda) in small doses and re-test after 30 minutes with jets running. If TA is high (above 120 ppm), add a pH-down product (sodium bisulphate or dry acid) slowly and aerate with jets to off-gas CO2. Aim for 90–110 ppm as a stable midpoint.
- 4
Correct pH, then sanitiser
Once TA is in range, check pH. Raise low pH with sodium carbonate (pH increaser) and lower high pH with sodium bisulphate — always add chemicals to water, never the reverse, and dose in small increments. After pH is stable at 7.2–7.6, adjust your sanitiser: add chlorine granules or a bromine tablet top-up to reach the target range. Shock the spa with a non-chlorine or chlorine shock dose once a week to oxidise organic waste and restore clarity.
- 5
Retest after 30 minutes and log the result
Run the jets for at least 15 minutes to dissolve and circulate any chemicals you have added, then wait a further 15 minutes before retesting. If any parameter is still outside range, make a second small adjustment and retest again — never add large doses in one go. Log the date, readings, and chemicals used in a simple notebook or spreadsheet. A log helps you spot drift patterns (for example, pH always dropping by Friday in summer) and adjust your routine proactively instead of reacting to a cloudy tub.
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FAQ
- How often should I test my spa water in summer in Greece?
- At least twice a week during heavy use, and always before and after a party or a group of guests. High air temperatures speed up chlorine loss and evaporation, which concentrates mineral levels — so summer demands more frequent checks than cooler months.
- Can I use the same test strips I use for my pool?
- Only if the strip explicitly lists all spa parameters, including the higher sanitiser range (up to 10 ppm) and calcium hardness. Many basic pool strips are calibrated for larger volumes and cooler water. Invest in spa-specific strips or a liquid drop-test kit for more reliable readings.
- My spa water keeps going cloudy even though the chlorine level looks fine — what is wrong?
- Cloudy water with acceptable chlorine usually points to either high pH (which reduces chlorine effectiveness), high total dissolved solids (TDS) after many weeks of top-ups without a water change), or biofilm building up in the plumbing. Shock the spa, clean the filter, and if cloudiness persists, drain, scrub, and refill with fresh water — in Greece, a full water change every 3–4 months is a sensible standard for a regularly used spa.