Water Hardness Problem

[The Piercer "Bob"]

Ok I just added 50 Channel Cat Fish a week ago, and I have been loosing 1-to 3 fish a day. I just found out that my well water is very Hard like 390 Alk is 232 my ph os 8.0.  My system has been cycling 8-weeks now, just drain my 30 gallon Bio-Filter yesterday and filled it back with my well water.  So what do I do to get this hardness down. Help. Thanks