Dittohead,
I've been saying 8 lbs for a long time but get shot down and made to look like I don't know what I'm talking about. When using 6 lbs, you must take out the reserve which means you really only have 16k worth of usable resin. I use 8 lb because it makes the math easier. Thanks.
California requires the systems be set for 6 pounds of salt per cubic foot of resin but we know that the quality of the softened water is greatly compromised at this low setting especially at the end of the run cycle. Hardness bleed by is a common complaint as the system nears its capacity the issue becomes even worse. Many systems come pre programmed at 4 pounds of salt per cubic foot, which causes considerable customer complaints as the water quality degrades beyond what is considered desirable.
Many years ago, we used to regenerate systems with 15+ pounds of salt per cubic foot per regeneration, this was very bad and wasteful. It should only be done on applications that require <3 PPM hardness like steam boilers. Even then, the softener should be installed in a primary and polisher design so as to maintain similar efficiency, but this is another topic...
Legally you may have to set your system to 6 pounds of salt per cubic foot, but the vast majority of installers bump that up to 8.
Removing the reserve? The reserve is an equation that is based on the singles days usage which is set so the system will regenrate prior to running out of capacity. I do regular training on system capacities, bleed curves, water quality expectations, etc. Wether you regenerate the system with 4 pounds or 18 pounds of salt per cubic foot, you still have to set your reserve, unless you are using proportional brining or twin alternating designs. Even with proportional brining, we recommend the programming have an intermittent "full salt" regeneration done at least every tenth regeneration. I beleive the Watts 7000 based unit does just this. Upflow brining may allow for some minor improvement on this issue, at least on paper, but in the real world, due to the regeneration cycles and the mixing of the bed that occurs prior to salting, and the 2nd backwash that is common on most new systems, the upflow regeneration has dropped in popularity due to the regulated brine complexities.
Most systems calculate the reserve or are easily adjusted so as to accomodate the system regardless of how many pounds of salt that are used. The 5600 "Econominder" still needs to be manually adjusted, but the important thing to remeber is to properly size the systems initially to maintain efficiency
Single tank systems should regenerate no more often than every fifth day, this will allow for acceptable efficiency. Anything past 5 days is more efficient, but only minimally so.
I didnt realize I as droning on this long.
Anyway, simple answer,
6# of salt per cu ft = 20,000 grains, but a hardness leakeage of 6-9 PPM is to be expected after regeneration, near the end of the systems capacity, leakage will increase considerably
8# of salt per cu. ft = 24,000 gains, hardness leakage of 3-4 PPM is to be expected after regeneration
By using a slightly higher amount of salt we have increased quality by 100%, and dropped our efficiency by 10%.