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 irregularshaped 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 irregularshaped 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 irregularshaped pool
Product Form  PH Stability  Available Chlorine  Common  
C1_{2} 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.) 

Highrate 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
Highrate sand filters are designed for flow rates of 5 to 20 gpm
Highrate 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 11/2″ 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 nonplumbed 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