Question 1

How much chlorine do I need to shock a 20,000 gallon pool?

Accepted Answer

To raise free chlorine from 0 ppm to 10 ppm (shock level) in a 20,000 gallon pool: Cal-Hypo 65% requires about 26 oz; Cal-Hypo 73% requires about 23 oz; Liquid chlorine 12.5% requires about 2.2 gallons; Trichlor requires about 23 oz. Use our calculator above for your exact current chlorine level and target.

Question 2

What is the difference between trichlor and cal-hypo?

Accepted Answer

Trichlor (90% available chlorine) is slow-dissolving and raises cyanuric acid (CYA/stabilizer) over time. Cal-Hypo (65% or 73% available chlorine) is a fast-acting shock that does not affect CYA but raises calcium hardness. In Miami where CYA can build up from year-round sun exposure, cal-hypo is often preferred for shock treatments.

Question 3

Can I mix trichlor tablets with cal-hypo shock?

Accepted Answer

NEVER mix trichlor and cal-hypo directly — this combination can cause fire, explosion, or release toxic chlorine gas. Always add chemicals to the pool separately, never together. Wait at least 30 minutes between adding different types of chlorine products.

Question 4

How long after adding chlorine can I swim?

Accepted Answer

Wait until free chlorine drops below 3 ppm before swimming. After a shock treatment (10 ppm), this typically takes 8–24 hours depending on sunlight and pool size. Always test with a test kit or test strips before allowing swimmers in the pool.

Question 5

Why does liquid chlorine degrade faster in Miami?

Accepted Answer

Liquid chlorine (sodium hypochlorite) loses potency rapidly when exposed to heat and UV light. In Miami's climate, liquid chlorine can lose 50% of its strength within a week if stored improperly. Always buy fresh product, store in a cool shaded area, and use within 30 days of purchase. This is why many Miami pool pros prefer cal-hypo granular shock for reliable potency.

Product	Available Cl	Form	CYA Impact	pH Effect	Best For
Trichlor Tablets (3")	90%	tablet	Raises CYA	Lowers pH (2.8)	Slow-dissolving 3" tablets for floaters and feeders.
Dichlor Granular	56%	granular	Raises CYA	Near neutral pH (6.7)	Fast-dissolving granular chlorine.
Cal-Hypo 65% Granular	65%	granular	No CYA	Raises pH (11.8)	Calcium hypochlorite granular shock.
Cal-Hypo 73% Granular	73%	granular	No CYA	Raises pH (11.8)	High-strength calcium hypochlorite.
Liquid Chlorine 10% (Bleach)	10%	liquid	No CYA	Raises pH (13)	Standard household/pool-grade sodium hypochlorite.
Liquid Chlorine 12.5% (Trade Grade)	13%	liquid	No CYA	Raises pH (13)	Professional-grade sodium hypochlorite.
Lithium Hypochlorite	35%	granular	No CYA	Raises pH slightly (10.8)	Lithium hypochlorite granular.

Pool Chlorine Demand Calculator

CHLORINE DEMAND CALCULATOR

Chlorine Product Comparison Guide

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