Water Chemistry

Chemistry Guide

Understand what each parameter means, why it matters, and how to keep your pool or spa in perfect balance.

Know Your Water

What Each Parameter Means

Each chemical parameter plays a specific role in keeping your water safe, comfortable, and equipment-friendly. Select any parameter to learn more.

Free Chlorine

Pool 1–3 ppm Spa 3–5 ppm

Free chlorine is the active sanitizer that kills bacteria, viruses, and algae in your pool or spa. It is the most critical parameter for water safety.

When free chlorine levels are maintained correctly, your water stays safe and clear. This is the portion of chlorine available to actively sanitize your pool, unlike combined chlorine which has already reacted with contaminants.

If too low: Risk of bacteria, algae growth, and waterborne illness. Water may turn green or cloudy.
If too high: Eye and skin irritation. Strong chemical smell. May bleach swimwear.
How to fix: Low: add chlorine shock or tabs. High: allow natural dissipation or use a chlorine neutralizer.

Total Chlorine

Pool 1–3 ppm Spa 3–5 ppm

Total chlorine is the combined measure of free chlorine and used (combined) chlorine. A large gap between total and free chlorine signals the need for shock treatment.

If your total chlorine is significantly higher than your free chlorine, it means chloramines (combined chlorine) have built up. Chloramines are the source of the strong "pool smell" and cause eye irritation, effectively trapping your chlorine from working.

If too low: Insufficient sanitization. Potential for algae and bacterial growth.
If too high: High combined chlorine (chloramines) causes the strong "pool smell" and eye irritation.
How to fix: Shock the water to break down chloramines and restore free chlorine levels.

Bromine

Pool 2–4 ppm Spa 4–6 ppm

Bromine is an alternative sanitizer to chlorine, popular for spas and hot tubs. It stays effective at higher temperatures and across a wider pH range than chlorine.

Unlike chlorine, bromine stays highly effective even at higher temperatures and across a wider pH range. Furthermore, "combined bromine" remains active as a sanitizer and does not off-gas strong odors, making it ideal for hot, indoor environments.

If too low: Inadequate sanitization. Risk of bacteria and algae growth.
If too high: Skin and eye irritation. Can corrode spa equipment over time.
How to fix: Low: add bromine tablets or granules. High: dilute with fresh water or allow natural dissipation.

MPS

Pool 3–8 ppm Spa 3–8 ppm

Monopersulfate (MPS) is a non-chlorine oxidizer that breaks down organic contaminants like sweat, oils, and cosmetics. It is widely used in spas and as a chlorine-free shock treatment.

It is widely used in spas and as a chlorine-free shock treatment for pools. MPS does not sanitize water (kill bacteria), but it oxidizes waste, which frees up your primary sanitizer to do its job more effectively.

If too low: Organic waste accumulates, reducing sanitizer efficiency and causing cloudy water.
If too high: Can interfere with chlorine and bromine test readings, producing false-high results. Wait 15 minutes before retesting.
How to fix: Low: add MPS shock. High: dilute with fresh water and retest after 15 minutes.

Peroxide

Pool 50–100 ppm Spa 50–100 ppm

Hydrogen peroxide (H₂O₂) is a natural oxidizing sanitizer used in chlorine-free pool and spa systems. It breaks down into water and oxygen, leaving no harsh chemical residue.

It provides a gentle alternative to traditional halogens and breaks down gracefully into water and oxygen, leaving absolutely no harsh chemical residue or byproducts in your water.

If too low: Insufficient oxidation. Bacteria and algae may develop.
If too high: Skin and eye irritation. May cause foaming or surface bleaching.
How to fix: Low: add a hydrogen peroxide-based pool product. High: dilute with fresh water or allow natural decomposition.

pH

Pool 7.2–7.6 Spa 7.2–7.6

pH measures how acidic or basic your water is on a scale of 0–14. The ideal range ensures sanitizers work at full strength and protects equipment and swimmers from corrosion and irritation.

Keeping pH in the ideal range ensures your sanitizers work at their theoretical full strength. Additionally, poorly balanced pH is the leading cause of eye and skin irritation, and can rapidly corrode equipment or scale surfaces.

If too low: Acidic water corrodes equipment, irritates eyes and skin, and rapidly degrades chlorine.
If too high: Basic water reduces sanitizer effectiveness, causing cloudy water and scale deposits on surfaces.
How to fix: Low pH: add pH Increaser (sodium carbonate). High pH: add pH Decreaser (sodium bisulfate or muriatic acid).

Alkalinity

Pool 80–120 ppm Spa 80–120 ppm

Total alkalinity acts as a pH buffer, preventing rapid pH swings. Keeping alkalinity in range makes pH much easier to maintain and protects surfaces from corrosion.

By absorbing major changes to the water chemistry before they affect the pH, keeping alkalinity in range makes your pH much easier to maintain. It also acts as second-line protection for your surfaces and equipment against corrosion.

If too low: pH becomes unstable and fluctuates rapidly. Corrosion of plaster, grout, and metal fittings.
If too high: pH becomes difficult to adjust downward. Cloudy water and scale on surfaces and heaters.
How to fix: Low: add Alkalinity Increaser (sodium bicarbonate). High: add pH Decreaser in small incremental doses.

Total Hardness

Pool 200–400 ppm Spa 150–250 ppm

Calcium hardness measures the amount of dissolved calcium in the water. Proper levels protect pool surfaces and equipment from both corrosion and mineral scale buildup.

Proper hardness levels protect pool surfaces and equipment. If water is too soft, it becomes aggressive and will leach calcium out of plaster and grout. If it is too hard, it will precipitate out and cause mineral scale buildup on surfaces and inside heaters.

If too low: Soft water is aggressive — it leaches calcium from plaster and equipment, causing etching and structural damage.
If too high: Scale deposits form on surfaces, equipment, and heaters. Water may turn cloudy.
How to fix: Low: add Calcium Hardness Increaser. High: partially drain and refill with fresh water.

Cyanuric Acid

Pool 30–50 ppm Spa N/A

Cyanuric acid (CYA), also called stabilizer or conditioner, shields chlorine from UV degradation. Without it, sunlight can destroy free chlorine within hours. Not typically used in covered spas.

Without CYA, intense sunlight can destroy a pool's free chlorine within just a few hours. However, too much CYA binds the chlorine too tightly, rendering it ineffective. CYA is not typically used or needed in covered spas away from direct sunlight.

If too low: Chlorine degrades rapidly in sunlight, requiring frequent additions to maintain safe levels.
If too high: Chlorine becomes far less effective ("chlorine lock"). Shocking becomes ineffective above 100 ppm.
How to fix: Low: add cyanuric acid (stabilizer). High: partially drain and refill — there is no chemical to reduce CYA.

Salt

Pool 3000–4000 ppm Spa 1000–2000 ppm

Salt is measured in pools with a salt-chlorine generator and some spa systems. The generator converts salt into chlorine automatically. Salt levels directly affect generator efficiency and output.

The generator uses an electrolytic cell to automatically convert dissolved salt into pure chlorine. Maintaining correct salt levels is vital, as it directly dictates the efficiency, output, and lifespan of your generator cell.

If too low: The chlorine generator runs inefficiently or shuts off. Manual chlorine supplementation may be needed.
If too high: Corrosion of metal fittings, ladders, and equipment over time. Water may have a slightly salty taste.
How to fix: Low: add pool-grade salt (sodium chloride). High: partially drain and refill with fresh water.

Phosphate

Pool < 200 ppb Spa < 200 ppb

Phosphates are nutrients that fuel algae growth. They enter water via fertilizers, decaying leaves, body care products, and tap water. High phosphates do not directly harm swimmers but make algae control much harder.

They are constantly introduced to water via fertilizers, decaying leaves, body care products, and even municipal tap water. While high phosphates do not directly harm swimmers, they make algae blooms much more frequent and significantly harder to control.

If too low: No concern — low phosphates actually help prevent algae blooms.
If too high: Algae blooms become more frequent and difficult to eliminate, even with correct chlorine levels.
How to fix: Apply a phosphate remover product. Identify and reduce the source: leaves, fertilizer runoff, or contaminated fill water.

Copper

Pool < 0.3 ppm Spa < 0.3 ppm

Copper enters pool water from copper plumbing, ionizers, or copper-based algaecide products. Trace levels can help inhibit algae, but elevated copper causes visible staining problems.

Trace levels of copper can actually help inhibit algae growth safely. However, elevated copper levels are highly problematic, reacting with chlorine to cause severe green, blue, or black staining on pool surfaces, equipment, and even blonde hair.

If too low: No concern at trace levels. Very low copper is normal and harmless.
If too high: Green, blue, or black staining on pool surfaces, equipment, and hair. Especially visible after chlorine shock.
How to fix: Use a metal sequestrant to bind copper and prevent staining. Reduce copper-based algaecide use. Consider a metal removal filter cartridge.