a whole house softener only removes the calcium and magnesium. In fact, water softeners actually increase the total dissolved solids (TDS) of the water so you actually have more crap in there.
If you want to reduce water hardness from 18 grains you will really need an RO system. I use tap water (330 PPM) and set buckets of water (4 gallons water, the rest filled with peat moss). This water is specifically for the Amazon Blackwater Stream for my Tetras, Rams, Appistos, Angels and Discus.
After a few days (4 or 5) of peat moss soaking in tap water, I can go from 330ppm hardness to 60ppm. Then I can use pH adjusters and buffers to get where I want to be. Two more days to let things settle (precipitate from the pH adjusters). Then I pump off the top 3 1/2 gallons and dispose of the 1/2 gallon that has all the particulate and settled matter. My system loses 1/2 gallon for every 4 gallons where my RO wastes 5 gallons for every 1 gallon because of all the TDS in the water.