size water softner

HELLO, I AM LOOKING FOR A WATER SOFTNER AND NEED HELP SELECTING THE RIGHT SIZE. WATER DEPARTMENT SAID OUR HARDNESS IS 233 MILLIGRAMS PER LITER OR 13.6 GRAINS PER GALLON. WE ARE USING 16,000 TO 20,944 GALLONS A MONTH. I HAVE BEEN LOOKING AT THE FLEC WATER SOFTNERS. I APPRECIATE YOUR HELP