Save your pool settings for quick calculations

Free Chlorine Calculator

Calculate how much liquid chlorine or bleach to add to your pool. Includes SLAM shock levels.

Pool Information

Don't know? Calculate it here
Cyanuric acid level from your test kit
0 5 10 15 20
Target Free Chlorine
ppm
Recommended for CYA 40
Liquid chlorine is recommended - no CYA buildup

Chlorine Dosage

Add this much -- fl oz
Also equals -- cups
Or in gallons -- gallons
Will raise FC to -- ppm
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FC/CYA Relationship: Based on your CYA of 40 ppm:
• Target FC: 5-7 ppm
• SLAM Level: 16 ppm
• Minimum FC: 3 ppm

Daily FC Maintenance Levels by CYA

Safe swimming range: 1-10 ppm FC (CDC recommendation)

Too Low
Minimum
Target Zone
0 2 4 6 8 10 12
Free Chlorine (ppm) - Daily Maintenance
High CYA Warning: If your CYA is above 80 ppm, consider a partial drain and refill. High CYA requires FC levels that approach or exceed safe swimming limits (10 ppm). Ideal CYA range: 30-50 ppm for most pools.

CYA & Chlorine Relationship Simulator

Understand why higher CYA requires more chlorine

The Science: Why Higher CYA Needs More Chlorine

When you add chlorine to your pool, it forms Hypochlorous Acid (HOCl) — the actual germ-killing, algae-fighting molecule. But CYA binds most of this chlorine, holding it in reserve:

HOCl + CYA ⇌ Cl-CYA + H₂O
(Active Chlorine) + (Stabilizer) ⇌ (Bound/Reserved Chlorine) + (Water)
Low CYA (30 ppm)
3%
97% bound
~0.05 ppm HOCl active
→
High CYA (80 ppm)
1%
99% bound
~0.02 ppm HOCl active
Key Insight: At 30 ppm CYA with 3 ppm FC, about 97% of your chlorine is bound to CYA. At 80 ppm CYA, that jumps to ~99% bound. To maintain the same killing power, you need proportionally more FC at higher CYA levels. This is NOT "chlorine lock" — it's chemistry working as designed!
ppm
ppm
(minor effect)
Your FC vs. Recommended Ranges for CYA 40
3
Min FC
5
Target FC
16
SLAM FC
0.04
Active HOCl
Target Zone

Your chlorine level is in the ideal daily maintenance range for your CYA level.

TFP Formulas (CYA = 40 ppm)

Minimum FC (7.5% × CYA)3.0 ppm
Target FC (~10% × CYA)4.0 ppm
SLAM FC (40% × CYA)16.0 ppm
Mustard Algae (60% × CYA)24.0 ppm

What is SLAM?

SLAM = Shock Level And Maintain

SLAM is the TFP method for killing algae and clearing a green pool. Unlike "pool shock" products, SLAM uses liquid chlorine and requires you to maintain shock-level FC continuously until the pool is clear.

SLAM Process:

  1. Raise FC to SLAM level for your CYA
  2. Run pump 24/7
  3. Brush pool daily
  4. Test and maintain FC every 2-4 hours during the day
  5. Continue until: water is clear, FC holds overnight, CC is 0.5 or less
Chlorine options: Liquid chlorine, cal-hypo, or dichlor/trichlor all work. Dichlor/trichlor add CYA - avoid consistent use and watch your CYA levels.