That's 17dGH or 27dGH (depending on which value you use); which is really hard. I'm not even sure if it's below safe standards?
I would either invest in an RO unit or if you live in the tropics then rain will do fine. Then again you live in Chicago, are you sure the water is free of sulfates? You can get an 6-stage RO unit for less than $150 if you're willing to spend. I mean with Discus, taking risks isn't much of an option.