Using The Saturation Index (Si) - Aquacal DIG-220 Owner's Manual

Basic Water Chemistry Continued:
CHEMICAL IDEAL IDEAL TEST
RANGE SCHEDULE
1 to 3 ppm Weekly
Free
Chlorine
7.2 to 7.8 Weekly
Ph
ppm
80 to 100 Monthly
Total
ppm
Alkalinity
3000 to 4500 Monthly
Salt
ppm
200 to 400 Monthly
Calcium
ppm
Hardness
60 to 80 ppm Monthly
Cyanuric
Acid (CYA)
- Stabilizer -
30 to 50 ppm

Using the Saturation Index (SI):

The Saturation Index is a formula used to predict the calcium carbonate saturation of water, that is, whether your water will precipitate, dissolve, or be in equilibrium with
calcium carbonate.
Water is properly balanced if the SI is 0 ± 0.3. If SI is greater than 0.3, scaling and staining will occur. If SI is less then -0.3, the water is corrosive to metallic fixtures and
aggressive to plaster surfaces and vinyl liners.
A high or low SI can cause premature damage to the cell, equipment or pool finish. As a general rule, higher concentrations of calcium, total dissolved solids, pH, and
alkalinity all promote a greater tendency for scale. Scaling potential also increases with increasing temperature.
Use the chart below to determine your overall water balance. Test water for pH, water temperature, Calcium Hardness, Total Alkalinity, Salt Level, and use the equivalent Factors
(TF, CF, AF, Constant) from the chart below to determine your Saturation Index. Adjust chemicals to maintain balanced water.
Corrosive to
metals, etches
plaster
finishes, and
irritates skin
REFERENCE SECTION
EFFECT OF LOW/HIGH LEVELS
Low free chlorine: Not enough residual chlorine to safely
sanitize pool water.
High free chlorine: Corrosive to metallic fixtures in pool water.
Can bleach swimwear and hair.
Low pH: (acidic) Equipment corrosion, eye/skin irritation,
plaster etching, rapid chlorine consumption.
High pH: (basic) Scale formation, cloudy water, eye/skin
irritation, poor chlorine effectiveness
Low TA: Eye irritation, pH "bounce", stained/etched plaster
and metal corrosion.
High TA: Constant acid demand, difficulty in maintaining pH,
and contributes to scale formation or cloudy water conditions.
Low Salt: Below 2,500 ppm causes premature cell failure and
reduces chlorine production
High Salt: Above 6,000 ppm can cause corrosion of metallic
fixtures and will taste salty. Note: DIG-220 can safely operate
with salt levels up to 35,000.
Low CH: Etching of plaster, equipment corrosion
High CH: Scale formation, cloudy water. Rapid buildup of
scale may exceed the system's self-cleaning capability
and require manual cleaning of the cell.
Low CYA: destruction of chlorine by the UV rays from the sun.
High CYA: Requires more chlorine to maintain proper sanitizer
levels.
Note: CYA not needed for indoor or bromine pool.
CYA can be reduced to 30 - 50 ppm for DIG-220 in colder
climate regions.
pH + TF + CF + AF - SC = SI
Calcium
TF
Temperature
Hardness
60 F 15.6C 0.4 150 ppm
66 F 18.9C 0.5 200 ppm
76 F 24.4C 0.6 250 ppm
84 F 28.9C 0.7 300 ppm
94 F 34.4C 0.8 400 ppm
103 F 39.4C 0.9 600 ppm
-.3 -.2
Low free chlorine: Check for combined chlorine level and shock
as necessary. Increase purifier output to maintain a 1-3 ppm
residual reading.
High free chlorine: Decrease purifier output. Let chlorine
dissipate normally until 1-3 ppm is achieved. In extreme
cases, pool water can be diluted with fresh water or a chlorine
neutralizer added. (Diluting will reduce salt and CYA. Check
and adjust as needed.)
Low pH: Add sodium carbonate or soda ash
High pH: Add muriatic acid or sodium bisulfate.
Low TA: Add sodium bicarbonate.
High TA: Add muriatic acid often, a little at a time (may take a
week or more to lower the TA).
Low Salt: Add salt according to digital display on Pool Pilot
unit or salt chart.
High Salt: If undesirably high, partially drain and refill the pool
with fresh water. (Diluting will reduce CYA. Check and adjust
as needed.)
Low CH: Add calcium chloride flakes.
High CH: Partially drain and refill pool with fresh water to
dilute. (Diluting will reduce salt and CYA. Check and adjust as
needed.)
Please note – in some areas there may be higher than
recommended calcium levels in the tap water. If this level is
seen, call the factory for advice on this condition.
Low CYA: Add cyanuric acid(1 lb/5000 gallons increases CYA
25 ppm)
High CYA: Partially drain and refill pool with fresh water to
dilute. (Diluting will reduce salt. Check and adjust as needed.)
Total
CF AF
Alkalinity
1.8 75 ppm 1.9
1.9 100 ppm 2.0
2.0 125 ppm 2.1
2.1 150 ppm 2.2
2.2 200 ppm 2.3
2.4 250 ppm 2.4
-.1 0 .1
OK
CORRECTIVE ACTIONS
SC
Salt Level
0 - 1000 ppm 12.1
1001 - 2000 ppm 12.2
2001 - 3000 ppm 12.3
3001 - 4000 ppm 12.4
4001 - 5000 ppm 12.5
5001 - 6000 ppm 12.6
.2 .3
Scaling,
staining, and
cloudy water
conditions
25