I'm still hoping for some sizing help. Here is what was recommended by a certain company located in the MidWest:

- Fleck 9100SXT Electronic 3/4 Inch Metered Twin Tank Water Softener 32000 Grain Capacity (Each Tank)
- (2) 9x48 Resin Tanks (Blue)
- 2.0 cubic feet of SST60 (Salt Saving Technology) Resin
- 9 gpm service flow rate
- 2 gpm backwash flow rate
- 3/4 Inch Noryl Yoke with Noryl Bypass Valve
- 15x17x36 Rect Brine Tank

Thanks.

First, a properly sized twin system will use no more or less salt or potassium chloride than a properly sized single tank system. What a twin tank system will do is cost more and use more water because they are generally sized to regenerate more often.

Prior to discharging your softener regeneration effluent to the surface, you need to check with your local authorities to see if it is permitted. Generally, surface discharge does not meet code.

Under very specific circumstances, SST-60 can reduce sodium/potassium usage by about 1/3. However, that requires you to use a very low salt dosage to regenerate, about doubling the size of softener you need. You also need to be aware that reducing the salt dosage results in more hardness bleed, which will change the feel of your softened water a bit. These aren't necessarily problems, but something to be aware of.

Before I make a size recommendation, you will need to decide if you really need a twin tank. I don't recommend it, but it's your call.

aliceinwonderland, thanks for your response.

Since I am re-using the water and since I am using the more expensive potassium pellets, I am trying to reduce salt usage as much as possible (also good for the environment).
My understanding of a twin tank system is it allows you to wait until the last minute to regenerate (vs. single tank systems that require some reserve of about 15-20% so that you can regen in the middle of the night to avoid sending hard water downstream). Is that a false assumption? If I can really reduce salt consumption even by 15%, then it is worth the extra expense of a second tank.
I am not so worried about how the water feels, as long as the water is soft - no longer have hard water stains on my granite countertops and my dishwasher does a better job. I am also installing a solar hot water so want to make sure not to foul that system.

Re: code compliance. I am not so worried about that since codes are very much behind the times. Laundry grey water recycling was just added to CA code a few years ago, though this is safe and practiced by many for decades. I am an engineer and very cautious, so if I run into problems I will run the regen cycle to the sanitary drain (via 3-way valve).

You will see closer to a 5% reduction using a twin system. The only way you would see close to a 15% reduction in salt usage is if somehow you always hit the cutoff right as you used the last drop of water for the day. Close, because twin tanks use softened water for brine make-up, which increases salt usage by a bit. You will save 2-3 lb potassium chloride per month using a twin vs single-tank system, assuming you regen with 4 lb salt/cuft of resin.

It is possible to regen with an even lower salt dosage, but not successfully in a standard softener. For that you would need a packed bed softener, such as those offered by Kinetico. They are mechanically operated by water power, rather than electronically controlled. Although they come at a premium price, they are very reliable. If your chief concern is environmental, they are worth a look.

The 2x1cuft twin system you have quoted above should work fine for your purposes if you prefer a Fleck softener. Alternately, a 1.5 cuft single tank would work.

For watering outdoor plants you may wand to consider alternating between raw water and softener effluent. The effluent will have a very high TDS. Coupled with your already high pH, it could burn your plants if it is their primary source of water. There is a big difference between watering with potassium-softened water and watering with potassium chloride saturated water.

Your comments have me thinking about mixing my regen water with my 300 gallon rainwater recycling tank tied to the gutters. But it is not very close to where I will install the softener.
How high and far can I run the regen drain line from the valve head? I have not found anything in the FLeck literature and have seen various numbers on the web. Some also say it is measured from the height of the valve, others say it is measured from the floor.