Domakihub How to Raise Pool Calcium Hardness Safely
Keep your pool water balanced so it never eats through plaster, grout, or equipment.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
Calcium hardness is one of the most overlooked numbers in pool chemistry, yet getting it wrong costs real money in damaged plaster, cracked grout, and corroded fittings. The video above walks you through the full balancing picture; this guide gives you the practical, step-by-step process for raising low calcium so your pool — whether a private residence, a holiday rental, or a hotel complex in Greece — stays safe for swimmers and gentle on surfaces. The Mediterranean sun and heat accelerate evaporation, which concentrates every chemical in the water, making regular testing non-negotiable during the long Greek swimming season.
Why Calcium Hardness Matters for Greek Pools
Calcium hardness (CH) measures how much dissolved calcium is in your pool water. The ideal range for most pools is 200–400 ppm (parts per million); vinyl-liner pools can tolerate the lower end (175–225 ppm), while plaster and concrete pools do best at 200–275 ppm. Water below 150 ppm becomes 'hungry' — it pulls calcium directly out of grout, plaster, and even metal fittings to satisfy its mineral deficit, causing pitting and etching that is expensive to repair.
In Greece, many pools are filled from municipal supply or private wells, both of which vary widely in hardness depending on the region. Coastal properties with desalinated or rainwater top-ups can drop to surprisingly low levels. Hotels and vacation rentals that run their pools continuously face the added challenge of dilution from splash-out and backwash, which must be offset by regular testing and dosing.
What You Need Before You Start
You will need: a reliable test kit or test strips that measure calcium hardness specifically (not just pH and chlorine), a bag or bucket of calcium chloride (CaCl₂) labelled as 'calcium hardness increaser', a 5-litre clean bucket, a pool calculator (many are free online) or the dosage chart on the product label, and protective gloves and eye protection. Calcium chloride dissolves exothermically — it generates heat — so never add it dry to the skimmer or directly to the pool without pre-dissolving it first, and never pour it near a vinyl liner without dilution.
How to Raise Pool Calcium Hardness: 5 Steps
- 1
Test the current calcium hardness level
Use a drop-count test kit or a reliable strip that includes a CH column. Collect the water sample from elbow depth (about 30 cm below the surface) away from the return jets. Note the reading in ppm. If you are below 150 ppm, you need to act immediately; between 150 and 200 ppm, plan a correction within the week. Always test early in the morning before the sun alters surface chemistry readings.
- 2
Calculate how much calcium chloride to add
Use the product label's dosage chart or a free online pool calculator. As a rough guide, 100 g of granular calcium chloride per 10,000 litres of pool water raises CH by approximately 10 ppm. Measure your pool's volume accurately — length × width × average depth × 1,000 for litres. For a typical 50,000-litre private pool starting at 100 ppm and targeting 225 ppm, you will need around 625 g, but always let the calculator confirm this.
- 3
Pre-dissolve the calcium chloride in a bucket
Fill a clean 5-litre bucket with pool water. Slowly pour the measured calcium chloride into the water — never the other way around. Stir until fully dissolved. The mixture will become warm; that is normal. Let it cool for two minutes before handling. Always wear gloves and safety glasses during this step, as the solution is caustic and spatters easily.
- 4
Add the solution slowly around the pool perimeter
With the circulation pump running, walk the perimeter of the pool and pour the dissolved solution in a thin, steady stream close to the water surface. Avoid pouring the entire amount into one spot, especially in pools with vinyl liners or painted surfaces. If you need to raise CH by more than 50 ppm, split the dose across two consecutive days to avoid overshooting and to reduce the temporary cloudiness that large single doses can cause in hot water.
- 5
Retest after 24 hours and adjust if needed
Allow the pump to circulate for at least four hours — ideally overnight — then retest CH the following morning. If you are still below target, repeat the calculation for the remaining deficit and add a second dose. Once you reach your target range (200–275 ppm for plaster pools, 175–225 ppm for vinyl), record the date and the volume added in your pool log so you can anticipate the next correction. Retest monthly during peak season.
Rather have a pro handle it?
Get a vetted pool pro in your city — one number, booked in EN/EL/DE.
FAQ
- Can I raise calcium hardness and adjust pH on the same day?
- It is best to adjust one parameter at a time and wait at least four hours between additions. Calcium chloride raises the pH slightly when it dissolves, so test pH after the CH correction has fully circulated before making any pH adjustments. Adding multiple chemicals simultaneously makes it harder to diagnose which one caused a problem if cloudiness or scaling appears.
- What happens if I accidentally overshoot and calcium hardness gets too high?
- Levels above 400–500 ppm cause calcium to precipitate out of solution, resulting in white scale on pool walls, cloudy water, and clogged filters. The only reliable remedy is partial draining and refilling with softer water. Prevention is far easier: always dose conservatively, split large corrections across two days, and retest before adding more.
- Does evaporation in the Greek summer affect calcium hardness?
- Yes — evaporation removes water but leaves all dissolved minerals behind, so calcium hardness (along with salt and other minerals) concentrates over time. During July and August, a pool can lose 3–5 cm of water per week to evaporation in Greece. When you top up with fresh water you dilute CH slightly, but the net effect across a hot season is usually a gradual rise, not a fall. This is why monthly testing is essential; you may find CH creeping upward rather than dropping, especially in pools not subject to heavy splash-out.