Aquarium chemistry HELP

My mom wanted to change up her big 170L (44gallon) tank with new landscaping, but she wanted the water chemistry to be fixed since her 2 angelfish started to get sick. But since doesn't understand English or know anything about chemistry I had to do the research and I f'd up. The first thing that was wrong was the pH since it was too low (too acid). I googled how to get it up and it recommended baking soda...my mom gave a green light so we added 7 teaspoons. We also did a 50L (13Gallon) waterchange to lower NO3. The next day we had 1 dead fish and everyone else were gasping for air. The pH was too high and KH had raised. I added a dose and half of Aquarium mineral and 4h later added 2doeses more. 4h later we did a small 13L (3gallon) water change and added acctimol plus 17ml of Catappa-X. By the next day everything was fine except NO3 and NO2 that were too high for the charts..We did a 80-60L waterchange (as much we could without leaving the filters out of water). We added 2 Anubias from separate tank, 2 bigger pieces of driftwood and 15ml of Catappa-X plus Detox. Throughout the night and early morning i was checking the water and added 500ml of detox in total through out 24h. Yesterday NO2 started going down, we added some new plants and surface plants and a potted plant to help with NO3 and NO2. Today morning they were again through the roof. In total...8 fish dead. The tank has been working for almost 3years ... is there any coming back or should we just start over?