Pool Tip #52: Recommended Pool Chemical & Natatorium Air Levels

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Oxidation reduction potential (ORP) 750 – 900 mV (Commercial)
650 mV (Residential)
865 mV (Cryptosporidium, Giardia and viral inactivation)
Free available chlorine 3.0 – 5.0 ppm or as needed to maintain a 750 mV ORP
Combined available chlorine < 0.3 ppm
Total available chlorine No more than 0.2 ppm higher than FAC
Total bromine 4.5 – 6.5 ppm or as needed to maintain a 750 mV ORP
Cyanuric acid 0 ppm (Indoors)
10 – 30 ppm (Outdoors)
UV Light Disinfectant level is related to light intensity and exposure time. UV dosage is measured in microwatt seconds per square centimeter (MWS/cm2). You may also see intensity and exposure time expressed in millijoules per square centimeter (mJ/cm2) instead. Six thousand to 10,000 MWS/cm2 or a minimum of 60 mJ/cm2are needed to destroy pathogenic organisms.Two types of UV lamps: low pressure (with an electromagnetic spectrum between 185 and 254 nanometers); and more commonly used today, medium pressure high intensity (with a wider electromagnetic spectrum between 180 and 400 nanometers, and not affected by water temperature). UV is most germicidal in wavelengths between 240 and 280 nanometers. Organic compounds are best photo oxidized by hydroxyl radicals in wavelengths below 230 nanometers. The bond between chlorine and nitrogen is broken, and chloramine destruction is most effective in the range of 245 and 340 nanometers, making low pressure bulbs a poor choice for chloramine destruction. Install downstream of the filters. Install UV monitor to measure intensity and lamp output over time. Equip with an indicator to show when the lamps are functioning. Replace on a 9 month to 1 year basis, or after 8,000 hours of continuous use. Operate continuously on a 24 hour basis.
Ozone Minimum 25 – 33% slip stream. Generator output should equal 4 – 6% ozone by weight concentration. Utilizes an oxygen prep unit, contact chamber (sized at gpm x 4), ozone destructor of either granulated activated carbon (GAC) or a manganese dioxide catalytic converter prior to introduction into the main stream and pool (chlorinated pools), and vents off–gassed air to the outside. ORP after the reaction tank > 850 mV.Sizing: Circulation flow rate in gallons per minute x 0.227 x dose rate in mg/liter (recommend 0.4 mg/l with 4 minutes of contact time in order to achieve a 1.6 CT value) = grams per hour
Polymeric biguanide (PHMB) 30 – 50 ppm
Salinity (Electrolytic cells) 2,500 – 6,000 ppm (4,000 ppm ideal)
Sulfates < 250 ppm
Hydrogen peroxide 30 – 40 ppm or as needed to maintain a 750 mV ORP
pH 7.2 – 7.8
Acid or base demand Neither
Total alkalinity 80 – 120 ppm
Calcium hardness 200 – 400 ppm
Total dissolved solids (TDS) < 1,500 ppm
Langelier saturation index 0 (+ or – 0.3 acceptable)
Ryznar Stability Index 6.3 – 6.7
Iron 0 – 0.2 ppm
Copper 0 – 0.3 ppm
Manganese 0 – 1.5 ppm
Nitrates < 10 mg/L (Uncontrollable algae growth at 25 mg/L)
Phosphates 0.2 – 0.5 maximum
Clarity Crystal clear
0.25 Nephelometric Turbidity Units (NTU)
0.2 Jackson Turbidity Units (JTU)
Water level

Skimmers Mid–point of skimmer weir
Gutters Constant overflow at quiescence
Turnover Time

6 hours (Multi–use and competitive swimming pools)
2 – 4 hours (Therapy pools, swim school pools, warm water pools or pools with heavy bather load to water volume ratios)
1 hour (Wading pools, activity pools, flume splash pools)
< 30 minutes (Spas)
Minimum 1,400 gallons per day to be circulated for each anticipated bather per day
Water level

Skimmers Mid-point of skimmer weir
Gutters Constant overflow at quiescence
Water circulation pattern Uniform circulation and absence of dead spots
Pipe sizing

Velocity = (0.32 x Flowrate in gpm) ÷ Pipe area in inches2
Discharge pipe 8 – 10 feet per second (maximum)
Suction pipe 6 – 8 feet per second (maximum)
Filter sizing (Design flow rate) Rapid sand
1.5 – 5.0 gpm/ft2 (3.0 gpm/ft2 typical)

High rate sand
10 – 15 gpm/ft2 (commercial), 20 gpm/ft2 (residential)

Multi–cell sand
3 – 7.5 gpm/ft2

Vacuum sand
0.5 gpm/ft2

Hi–rate bi–flow vacuum sand
6.25 – 15 gpm/ft2

Diatomaceous earth
1.5 – 2.0 gpm/ft2 (commercial), 2.5 – 3.0 gpm/ft2 (residential)

Cartridge
0.375 gpm/ft2 (commercial), 1.0 gpm/ft2 (residential)
Water temperature

104° F (Maximum spas)
86° – 94° F (Therapy pools)
78° – 82° F (Competitive pools)
83° – 86° F (Multi–use pools)
Air temperature 2° – 7° F above pool water temperature
Compliance with ASHRAE Standard 55–1992: “Thermal Environmental Conditions for Human Occupancy”
Relative humidity 50 – 60% maximum
Ventilation 0.5 cfm of outside air for each square foot of natatorium area15 – 25 cfm for each person in the natatoriumAt least 6 and preferably 8 complete air exchanges per hourMaintain CO2 levels below 0.1% or 1,000 ppmPercentage of fresh air introduced: Recommended minimum 40%, maximum 100% depending on usage patterns, natatorium design, and equipment installed
Air distribution Air introduced from low to high, passed over the water surface
No noticeable drafts of temperature gradients
Compliance with ASHRAE Standard 62–1989: “Ventilation for Acceptable Indoor Air Quality”
Pressurization Natatoriums should be positively pressured in relation to the out of doors, and negatively pressured in relation to surrounding occupied spacesNote: Pollutants travel from positive to negative pressure areas
Chemicals in air 6″ over the pool

Chlorine 1.0 ppm maximum TWA,
0.5 ppm TLV–TWA
30 ppm IDLH
Bromine 1.0 ppm TLV–TWA
10 ppm IDLH
Ozone 0.1 ppm maximum TWA
Carbon dioxide 5,000 ppm TLV–TWA
Chloroform 10 ppm TLV –TWA
Total coliforms Membrane filtration technique:
< 1 colony per 100 millilitersMultiple tube fermentation method:
None – fewer than 15% of samples in the seriesPresence – absence test:
AbsentStandard agar plate count:
< 200 bacteria per millimeter
Standard (Heterotrophic) Plate Count Colony forming units (CFU) < 200 colonies per milliliter
Pseudomonas aeruginosa

Membrane filter technique: < TNTC
Presence – absence test: Absent
Acoustics Reverberation time 0.8 – 2.4 seconds to drop to 60 decibels
Illumination level 6″ over pool 100 footcandles (Indoors)
60 footcandles (Outdoors)