Pool Formulas 2017-05-03T16:53:39+00:00

Pool Formulas

FACTS AND FORMULAS

Length x width x average depth x 7.5 = volume (in gallons) of square or rectangular pool
3.14 (pi) x radius squared x average depth x 7.5 = volume (in gallons) of a round pool
0.45 x (A+B) x length x average depth x 7.5 = volume (in gallons) of kidney or irregular-shaped pool

Length x width x average depth x 7.5 = volume (in gallons) of square or rectangular pool
3.14 (pi) x radius squared x average depth x 7.5 = volume (in gallons) of a round pool
0.45 x (A+B) x length x average depth x 7.5 = volume (in gallons) of kidney or irregular-shaped pool

Length x width x average depth x 7.5 = volume (in gallons) of square or rectangular pool
3.14 (pi) x radius squared x average depth x 7.5 = volume (in gallons) of a round pool
0.45 x (A+B) x length x average depth x 7.5 = volume (in gallons) of kidney or irregular-shaped pool

Product Form PH Stability Available Chlorine Common
C12 gas Low 100% Gas very unstable
Sodium hypochlorite 13+ 12.5% Liquid unstable
Calcium hypochlorite 11.5 65% Dry granular stable
Dichlor 6.8 60% Dry granular very stable
Trichlor 3.0 90% Tablet (or granular) very very stable

1 pound C12 gas = 1 gallon sodium hypochlorite = 1.5 pounds calcium
Hypochlorite = 1.75 pounds dichlor = 1.15 pounds trichlor = 2.8 pounds lithium hypochlorite

Sodium hypochlorite = 2 times the cost of chlorine gas
Sodium hypochlorite = 2 times the cost of chlorine gas
Calcium hypochlorite = 3 times the cost of chlorine gas
Dichlor = 5 times the cost of chlorine gas
Trichlor = 3 times the cost of chlorine gas
Lithium = 5 times the cost of chlorine gas

95% of chlorine in water can be lost on a sunny day in two hours (without stabilizer).

Item Raise or Lower 10 ppm Product
Product Amount Required (dry weight unless otherwise noted)
Calcium hardness Raise Calcium Chloride 2 ounces
Total Alkalinity Raise Bicarb of Soda 2.5 ounces
Total Alkalinity Lower Sodium Bisulfate (dry acid) 2.5 ounces
Total Alkalinity Lower Muriatic Acid 1/4 Cup (Liquid)
Stabilizer Raise Cyanuric Acid 1.5 ounces
Availability of Product (Percent) Product Amount
12 1/8 Cup (Liquid)
50 1/4 Ounce (dry weight)
80 1/6 Ounce (dry weight)

Water may not move at more than 8′ per second through copper pipe.
Water may not move at more than 7′ per second through PVC (Some pipe manufacturers will not warranty over 5′ per second do to concerns over water hammer.)
Water may not move at more than 6′ per second through any type of suction pipe.

Gallons to Liters   Gallons x 3.785 = Liters
Liters to Gallons   Liters x 0.2642 = Gallons
Ounces to Milliliters   Ounces x 29.57 = Milliliters
Milliliters to Ounces   Milliliter x 0.0338 = Ounces
Inches to Millimeters   Inches x 25.4 = Millimeters
Filter Style Maximum Flow (gpm/sq. ft.)
Minimum Backwash Flow (gpm/sq.ft.)
High-rate sand 15 15
DE 2 2
Cartridge 0.375* No Backwash

*Note that cartridge filters are rated at 1 gpm/square foot maximum flow rate on most residential applications and the more stringent 0.375 gpm/square foot on commercial installations

Rapid sand filters are designed for flow rates of less than 3 gpm
High-rate sand filters are designed for flow rates of 5 to 20 gpm
High-rate sand filters are designed for flow rates of 5 to 20 gpm
The normal filter operating pressure differential (between incoming pipe and outgoing) is between 2 and 4 psi. When it reaches 10 psi, the filter must be cleaned. Expressed another way, if you know the normal operating pressure of your filter (as observed on the pressure gauge), you must clean the filter when the pressure is more than 10 psi higher.
Water flow must not exceed 100 gpm through 1-1/2″ heater plumbing
Water flow must not exceed 125 gpm through 2″ heater plumbing
Water flowing out of a heater should not be more than 10°F warmer than the water flowing into the heater
Pool water should not exceed 82°F
Spa water should not exceed 104°F
The on/off switch of a millivolt heater must not be located more than 20′ from the heater

The rear and non-plumbed sides must have a least 6″ of clearance
The plumbed side must have a least 18″ of clearance
The front must have at least 24″ of clearance
The top must be at least 5 feet below (and 4 feet horizontal distance) any window, door or vent
PVC gas lines must be buried at least 18″ below ground (12 inches below concrete)
Metal gas lines must be buried at least 12″ below ground (6 inches below concrete)

Chlorine Residual   1.0 to 3.0 ppm
Total Alkalinity   80 to 150 ppm
pH   7.4 to 7.6
Hardness   200 to 400 ppm
Total Dissolved Solids   Less than 2000 ppm
Cyanuric Acid   30 to 80 ppm

75% of the surface area of a pool is the required surface area of solar panels to adequately heat the pool
Each spa jet requires flow of 15 gpm
Each spa jet requires 1/4 hp from the pump and motor
To estimate the horsepower of a blower:

1 hp = 6.5 amps at 110 volts = 3.25 amps at 220 volts
2 hp = 13 amps at 110 volts = 6.5 amps at 220 volts
Volts x amps = watts
Heater BTU output rating divided by (gallons x 8.33) = degrees temperature rise/hour
Breakpoint chlorination method (for every 20,000 gallons of water):

1 gallon of anhydrous ammonia + 8 gallons liquid chlorine
Leak water loss conversion inches to gallons

Water loss in inches x (Surface Area divided by 100) x 62.5 = loss