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XI. Guidelines for Using ORP for
Water Maintenance
Q.
Why should I maintain a pH level between 7.4 and 7.6?
A.
pH levels below 7.4 can cause eye irritation, metal cor-
rosion, etching of plaster, stains, damage to vinyl liners,
and loss of sanitizer. In addition to eye irritation, pH lev-
els above 7.6 can cause cloudy water, scale formation
and loss of sanitizer efficiency (low ORP).
Q.
How do I increase the pH level?
A.
Small amounts of basic (alkaline) chemicals such as pH
Plus or pH Up can be added.
Q.
How do I lower the pH level?
A.
Small amounts of liquid acid (muriatic) or dry acid (sodi-
um bisulfate) such as pH Minus or pH Down can
be added.
Q.
How does 650 mV relate to the ppm of chlorine?
A.
Pure water, without conditioner, at a pH level of 7.5 cor-
responds to approximately 1.5 ppm of chlorine. Actual
pool or spa water usually takes at least 1-2 ppm of chlo-
rine to generate 650 mV ORP, although the Total
Dissolved Solids and pH can affect the activity of the
chlorine and thus change the level of ORP.
Q.
Does an ORP of 650 mV stop algae?
A.
No. Because algae is a living organism that adapts
genetically to a constant level of sanitizer, the periodic
addition of an algicide or shocking may be necessary.
Please note that the addition of some chemicals can
change the ORP readings for up to several days.
Q.
What causes a low ORP?
A.
A low sanitizer level, a pH level above 7.6, a conditioner
level above 200 ppm or a TDS (Total Dissolved Solids)
above 3,000 ppm can all cause a low ORP.