Pool Chemistry Cheat Sheet: Print This and Put It in Your Truck

Q: What are the ideal pool chemistry ranges?

Standard residential pool target ranges: Free Chlorine 2–4 ppm (adjusted for CYA — see FC:CYA table), pH 7.4–7.6, Total Alkalinity 80–120 ppm, Calcium Hardness 200–400 ppm, CYA (outdoor pools) 30–50 ppm, Combined Chlorine below 0.2 ppm, LSI between -0.3 and +0.3. Commercial pools follow tighter regulatory ranges: FC minimum 1 ppm (most states), pH 7.2–7.8, CC below 0.5 ppm.

Q: What is the minimum FC for each CYA level?

Minimum FC = 7.5% of CYA. At 30 ppm CYA, minimum FC is 2.3 ppm. At 40 ppm CYA, minimum FC is 3.0 ppm. At 50 ppm CYA, minimum FC is 3.75 ppm. At 60 ppm CYA, minimum FC is 4.5 ppm. At 80 ppm CYA, minimum FC is 6.0 ppm. At 100 ppm CYA, minimum FC is 7.5 ppm (partial drain recommended at this CYA level).

Q: Which pool chemicals should never be mixed together?

Never mix: (1) Trichlor and cal hypo — violent reaction, fire/explosion risk. (2) Any chlorine product with muriatic acid — produces chlorine gas. (3) Different brands of chlorine tablets — may use different formulations. (4) Chemicals in an undiluted state — always dissolve granulars in water before adding to pool. Add chemicals to water, never water to chemicals.

📅 May 21, 2026Pool Pro⏱ 5 min read

This is the reference page. Every target range, every formula, every table you find yourself looking up in the field — collected in one place. Bookmark it, print it, or access it offline in PoolLens. These are the numbers and rules that every pool service professional should have immediate recall of, and this is the resource to build that recall from.

Core Parameter Target Ranges

Parameter	Residential Target	Commercial Target	Notes
Free Chlorine (FC)	Per CYA table below	1 ppm minimum (most states)	Never let FC drop to zero
Combined Chlorine (CC)	Below 0.2 ppm	Below 0.5 ppm	CC above 0.5 = shock needed
pH	7.4–7.6	7.2–7.8 (per health code)	Target 7.4–7.5 for best HOCl activity
Total Alkalinity (TA)	80–120 ppm	80–120 ppm	80–100 with CO2 systems
Calcium Hardness (CH)	200–400 ppm	200–400 ppm	150–250 for vinyl liner pools
CYA (outdoor pools)	30–50 ppm	0–50 ppm (varies by code)	Many commercial codes limit or ban CYA
LSI	-0.3 to +0.3	-0.3 to +0.3	Provide pool temp when submitting to lab
Salt (salt pools)	Per cell specs (2,700–3,500 ppm)	Per system specs	Test monthly; verify with standalone meter

FC:CYA Minimum Free Chlorine Table

Minimum FC = 7.5% of CYA. SLAM/shock FC = see third column.

CYA (ppm)	Minimum FC	Shock Level (SLAM)	Algae Risk Below Minimum
20	1.5 ppm	12 ppm	Low (no CYA protection)
30	2.3 ppm	15 ppm	High if FC at 1 ppm
40	3.0 ppm	20 ppm	High if FC at 1–2 ppm
50	3.75 ppm	24 ppm	Very high if FC below 3 ppm
60	4.5 ppm	28 ppm	Very high
80	6.0 ppm	31 ppm	Extreme — consider partial drain
100+	7.5+ ppm	40+ ppm	Drain 25–30% and refill

Chemical Safety — Never Mix

NEVER mix: Trichlor + Cal Hypo (fire/explosion). Any chlorine + muriatic acid (chlorine gas). Different chlorine products. Always add chemical to water, not water to chemical. Add chemicals to pool while pump is running — never simultaneously.

Breakpoint Chlorination Formula

Minimum shock FC = CC × 10

Example: CC = 0.8 ppm → minimum shock = 8 ppm FC. Below breakpoint, adding chlorine creates MORE chloramines before destroying them. You must exceed breakpoint to destroy CC.

HOCl% by pH — Why pH Matters for Chlorine Effectiveness

pH	HOCl % (Active Killing Form)	OCl- % (Weak Form)
7.0	~72%	~28%
7.2	~60%	~40%
7.4	~45%	~55%
7.6	~28%	~72%
7.8	~18%	~82%
8.0	~9%	~91%

LSI Factors (Simplified)

LSI = pH + TF + CF + AF − 12.1

Temperature	TF	CH (ppm)	CF	TA (ppm)	AF
60°F / 16°C	0.0	100	1.6	60	1.7
68°F / 20°C	0.1	150	1.8	80	1.9
77°F / 25°C	0.3	200	1.9	100	2.0
86°F / 30°C	0.5	300	2.1	120	2.1
95°F / 35°C	0.6	400	2.2	150	2.2
104°F / 40°C	0.8	600	2.4	200	2.3

Key Rules to Memorize

FC:CYA minimum — FC must be at least 7.5% of CYA
Breakpoint chlorination — shock to at least 10× CC to destroy chloramines
pH-HOCl relationship — every 0.3 unit rise in pH roughly halves HOCl fraction
CYA cap — above 80–100 ppm, partial drain is the only fix
LSI targets — -0.3 to +0.3 is balanced water
Salt pool pH — salt systems continuously push pH up; expect more acid use than non-salt pools
TA and pH interaction — high TA causes pH to resist downward adjustment and bounce back; 80–100 ppm TA makes pH easier to manage
CYA and SLAM — during SLAM, maintain FC at shock level (see table) 24 hours a day until overnight chlorine loss is below 1 ppm and water is clear

Common Chemical Compatibility Reference

Chemical	Raises	Lowers	Also Affects
Sodium bicarbonate (baking soda)	TA	—	Slight pH rise
Sodium carbonate (soda ash)	pH	—	Slight TA rise
Muriatic acid	—	pH, TA	Lowers both
Calcium chloride	CH	—	Slight TDS rise
Cyanuric acid	CYA	—	Slight TA lowering effect
Liquid chlorine (NaOCl)	FC, pH	—	Slight TA rise long-term
Trichlor tablets	FC, CYA	pH	Slow CYA accumulation
Cal hypo granular shock	FC, CH	—	CH rise over time

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Frequently Asked Questions

What are the ideal pool chemistry ranges?

Standard residential pool target ranges: Free Chlorine adjusted for CYA (see FC:CYA table), pH 7.4–7.6, Total Alkalinity 80–120 ppm, Calcium Hardness 200–400 ppm, CYA 30–50 ppm for outdoor pools, Combined Chlorine below 0.2 ppm, LSI between -0.3 and +0.3.

What is the minimum FC for each CYA level?

Minimum FC = 7.5% of CYA. At 30 ppm CYA: 2.3 ppm minimum FC. At 50 ppm CYA: 3.75 ppm. At 80 ppm CYA: 6.0 ppm. At 100 ppm CYA: 7.5 ppm minimum — partial drain recommended at this level.

How do you calculate the Langelier Saturation Index?

LSI = pH + TF + CF + AF - 12.1. Where TF is the temperature factor, CF is the calcium factor based on CH ppm, and AF is the alkalinity factor based on TA ppm. Ideal LSI is between -0.3 and +0.3. Above +0.3 = scaling tendency. Below -0.3 = corrosive tendency.

Which pool chemicals should never be mixed together?

Never mix: trichlor and cal hypo (violent reaction, fire risk), any chlorine product with muriatic acid (chlorine gas), or different brands of chlorine products. Always add chemical to water, never water to chemical. Add chemicals to pool while pump is running — never simultaneously.