Assume 60 gallons of water per day per person (natural average) if iron is present: multiply ppm x 2 and add hardness to arrive at compensated hardness. Iron is more readily exchanged than hardness and this method compensates the softener capacity.
Example: Number of Persons x 60 x Comp. Hardness = Grains Capacity Used Per Day.
Multiply: Grains per Day x 3 Days = Approximate Capacity of Softener Required. The number of days may be extended to arrive at a catalog unit which will not exhaust before regeneration.
4 persons in household
18 grains hardness
1.5 ppm iron (clear water)
Compensated Hardness = 1.5 x 2 + 18 = 21 grains
4 x 60 x 21 = 5040 grains/day x 3 days = 15,120 grains capacity ML-15S (15,000 grain capacity) is too small. Timer can only be set for: Once/6 days, Twice/6 days, Three times/6days. (Cannot be set for every 4th or 5th day.)
ML-22D (22,000 gr.) = 4.36 Days (too large) ML-25S (25,000 gr.) = 4.96 Days (too large) ML-30D (30,000 gr.) = 5.95 Days (too small)
Due to limitation of time clock there is not an efficient choice. The closest time clock unit would be a ML-22D. Consider metered (MP) unit: MP-25S (4.96 days average) or MP-36D (7.143 days average).