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Algae: Microscopic forms of plant life, which can enter the pool or spa.  There are numerous varieties-some are free floating, others grow on walls and surfaces.

Algicides: Chemicals that prevent and control algae.  Non-foaming types are recommended for spas.

Bacteria: The germs that can contaminate your pool, spa or hot tub. Introduced primarily by users.

Balanced water: The correct ratio of mineral content and pH level that prevents pool and spa water from becoming corrosive or scale forming.

Bromamines: compounds formed when bromine combines with nitrogen from urine, perspiration, etc.  Relatively effective sanitizers.

Bromine: A spa sanitizer in the same family as chlorine.  Used in a granular or convenient compressed form for continuous treatment.

Calcium Hardness: The amount of dissolved calcium in spa water.  This should be approximately 100-200 ppm.  Higher levels can cause cloudy water and scale.  Lower levels can harm the spa and its equipment.

Cartridge Filter: The most widely used spa water filter.  Uses paper or fabric-like cartridges as its removal system.

Chlorine: An efficient sanitizing chemical for pools or spas.  The primary type used for spa care is granular stabilized, organic chlorine.  This type is totally soluble and nearly pH neutral.

Chloramines: Compounds formed when chlorine combines with nitrogen from urine, perspiration, etc.  Chloramines cause eye and skin irritation, as well as strong chlorine odors.

Chlorine (or Bromine) Demand: The amount of chlorine or bromine that must be added before a chlorine or bromine residual can be maintained.

Chlorine (or Bromine) Residual: the amount of chlorine or bromine remaining after chlorine or bromine demand has been satisfied.  This is the reading obtained with your test kit.

Corrosion: Deterioration of metal surfaces caused by low pH, low total alkalinity, low calcium hardness or a combination of the three.  High velocity in spas can cause erosion.

Dry Acid: slowly lowers pH and total alkalinity.  Safer to handle and easier to accurately measure than liquid acid.

Free Chlorine: Also called available, usable chlorine.  It’s the most active form of chlorine free to kill bacteria and algae.

Nitrogen: An element introduced into the spa via urine, perspiration, hair spray, cosmetics, etc.  Reduces the effectiveness of sanitizers and forms skin and eye irritating chloramines.

OTO: A liquid solution used in some test kits to measure total chlorine.  It can’t distinguish between free available chlorine and chloramines, so it’s less desirable than DPD.

pH: The measure of acidity and alkalinity.  Should be 7.4 to 7.6.  Below 7.0, water is acidic and will corrode equipment and can damage some pool/spa surfaces.  Above 7.8 the water’s too alkaline- cloudiness and scale formation may result.  Improper pH also affects sanitizer’s germ killing power and can cause discomfort for users.

 ppm: An abbreviation for “parts per million”, the accepted measurement of chemical concentration in spa water.

Phenol Red: A chemical reagent used in testing for pH.  Has effective range of 6.8 to 8.4.

Reagent: Chemical material in liquid, powder or tablet form for use in chemical testing.

Scale: Sandpaper-like calcium bearing deposits that can coat pool/spa surfaces and clog filters, heaters and plumbing.  Generally caused by mineral content combined with high pH and enhanced by hot water.

Stabilized Chlorine: Contain stabilizer to provide longer lasting protection for the pool, meaning fewer applications and less expense.

Stabilizer: Stabilizers prevent sunlight from dissipating chlorine strength and reduce the amount used in a season.

Superchlorination: Also known as shock treatment or oxidation.  A process of adding significant doses of quick dissolving oxidizing chemical to destroy non-filterable organic wastes.

Total Alkalinity: The amount of carbonate, bicarbonate and hydroxyl ions in spa water.  Total alkalinity affects and controls pH.  If total alkalinity is high, pH will be hard to adjust.  If it’s too low, pH will be unstable, difficult to maintain within desired range.  This should be 125 to 150 ppm in spa water.