Hi, I'm new to the site and new to discus keeping. I've had my tank up for about six weeks now and in that time have lost my four discus who I put into the tank about two and a half weeks after running a fish less tank. I was constantly getting a high pH reading of around 7.6 and plus so had advice from the pet shop and tried all these different chemicals for the tank to ultimately crash and my discus to die (eight days ago) I've since done some research on water hardness, bought a kit to test the tank water hardness to find that my water hardness was way off the charts. Subsequently I've siphoned 66 litres of the 220 out and replaced it with tap water which I've treated with api tap water conditioner. The levels have dropped 24 hrs later to

KH 125.3
GH 179

I'm aware that Discus do best in 0-50 ppm

Wondering if anyone has experienced similar hardness and how they fixed it. I want to get the tank to a suitable quality so I can put discus back in and keep them healthy. Any advice would be much appreciated.