Alkalinity is probalby the easiest test measurement to correct in relation to your swimming pool. Your Alkalinity will be effected greatly by any rain. It is very unusual to have a neutral rain so it will either be a base or acid. Either way it will tend to lower or raise the Alkalinity. If the change in Alkalinity is caught early enough it will not be allowed to effect any other perameters, however, any change in Alkalinity which removes it from it's balanced range of 90-110 ppm will allow the pH measurement to go into a state classed as "pH bounce" which effectively means the pH will increase or decrease at will until it is stabilized along with the Alkalinity.
In effect the Alkalinity is a set of handcuffs which stabilize the pH.
To raise Alkalinity add Sodium Bicarbonate directly to the deep end of the pool, it is not necessary to have the filtration system running. 1.5lbs of Sodium Bicarbonate will raise the Alkalinity by 10 ppm in a 10,000 gallon pool.
Additions of large amounts of Sodium Bicarbonate can temporarily cloud the pool but this cloudiness will generally disipate within a few hours.
Bob Charlton is a Certified Pool & Spa Operator and Inspector with the National Swimming Pool Foundation with 17 years of experience within the pool industry in Florida.