Pool Chemical Dosage: A Cubic-Meter Guide to Chlorine, pH and Algaecide

The target free chlorine concentration for private pools is 1.0–3.0 ppm (mg/L). Concentrations below 1.0 ppm result in inadequate disinfection, while levels above 3.0 ppm cause eye and skin irritation. Aiming for 1.5–2.0 ppm is the ideal operational sweet spot for most pools.

In routine chlorination, raising free chlorine by 1.0 ppm requires approximately 15–18 grams of 56% sodium dichlor granules per 10 m³ of water. For a 48 m³ pool, raising chlorine by 1 ppm requires roughly 75–85 grams. During hot summer peaks, test water daily at sunset when UV degradation stops.

Shock (superchlorination) elevates chlorine to 5.0–10.0 ppm to eliminate refractory chloramines, bacteria, and algae spores. Shock dosing uses 10–20 grams of rapid-dissolving chlorine per m³, applied at dusk with continuous filtration overnight. Never swim until chlorine drops below 3.0 ppm.

pH measures water's acid-base equilibrium and acts as the master regulator of pool chemistry. The target range is strictly 7.2–7.6. Outside this band, chlorine efficacy drops precipitously: at pH 8.0, chlorine loses over 50% of its sanitizing power. Dosing chlorine without balancing pH first is like carrying water in a perforated bucket.

When pH rises, pH Minus (sodium bisulfate or dilute acid) is dosed. As a baseline rule, lowering pH by 0.2 units in 10 m³ requires roughly 100–150 grams of pH Minus, depending on total alkalinity. When pH is low, pH Plus (sodium carbonate) is added. Circulate water 4–6 hours before re-testing.

Total Alkalinity (TA) must be monitored alongside pH; the target range is 80–120 ppm. Alkalinity acts as the chemical buffer stabilizing pH: when TA is balanced, pH remains steady; when TA is low, pH fluctuates wildly. Stabilize alkalinity first to lock in pH.

Algaecide is a preventative barrier, not a standalone cure. Once active algae bloom establishes, algaecide alone cannot clear it; its function is inhibiting algae spores from germinating. Algaecide must be used as a routine weekly preventative.

Standard preventative maintenance dosing is 3–5 ml of non-foaming algaecide per m³ weekly (approx. 150–250 ml weekly for a 48 m³ pool). A higher initial dose (8–10 ml/m³) is applied at spring opening. Dose algaecide with pumps running for uniform distribution.

Always specify non-foaming algaecides; low-grade products create persistent surface foam and oil sheens. AstralPool chemical lines provide concentrated, non-foaming algaecides engineered for luxury and commercial pool applications.

Chemical sequencing is just as critical as dosage. Adding chemicals in the wrong sequence can neutralize active ingredients or produce dangerous chemical reactions. The correct protocol: first balance Total Alkalinity and pH; once water stabilizes, dose chlorine; and finally add algaecides or clarifiers.

Never mix different dry or concentrated liquid chemicals together. Always add each chemical separately directly into the pool over return jets with the pump running, allowing at least several hours between treatments.

Always add chemicals to water, never water to concentrated chemicals. Dissolving granular products in a clean bucket of pool water prior to distribution prevents concentrated granules from settling onto and bleaching PVC liners or colored mosaic grout.

If you add chlorine continuously but test kits consistently show zero free chlorine while water smells pungent, your pool is likely experiencing 'chlorine lock.' The primary culprit is excessive cyanuric acid (CYA), the stabilizer used in trichlor tablets.

While ideal CYA is 30–50 ppm to protect chlorine from sunlight UV breakdown, levels exceeding 80–100 ppm over-stabilize the water, binding chlorine so tightly that it can no longer disinfect. Stabilized tablet users inadvertently build up CYA because stabilizer never evaporates.

There are no chemical removers for cyanuric acid; the only solution is draining a portion of pool water and refilling with fresh water. Prevent chlorine lock by alternating stabilized tablets with unstabilized liquid chlorine and testing CYA monthly.

Even perfect dosing calculations fail if testing is inaccurate. Always collect water samples at elbow depth (approx. 40 cm below surface) away from return jets and skimmer mouths; surface water does not reflect bulk water chemistry.

Chemical reagents degrade over time; replace test tablets and liquid reagents annually and store testing kits in a cool, dark cabinet. DPD photometers or liquid drop kits provide far greater precision than test strips for critical balancing.

Never test immediately after adding chemicals; allow 4–6 hours of continuous filtration for complete homogenization. Testing prematurely leads to false readings and accidental double-dosing.