What are symptoms of hard water? does using carbon make your water softer/harder? Also what is the best test kit to check your water parameters GH and KH. Thanks
Hard water is easy to spot visually. You'll probably notice it around your bathroom first... bathtub and faucets would show it. API generally makes the best kits.
Check your cities website too, they may publish yearly reports on your water. With the exception of expense and hassle of going RO there not much you can do about hard water.
In Chicago, our water is pretty much liquid rock its chimes in at around 280 GH. Other than the stains on the tank glass theres not much effect on the turtle.