Marylyn

Hi all, I need help. I have several tanks but I am only having problems in my guppie tank. I had hard water and we went with a water softener. I use the bypass when filling the tanks but the hot water is soft. I have lost 3 guppies this week. My ph is 7.8 right now. I use a python to do my water changes. Will I have to go back to using a bucket? I also put prime in when I change the water. Please help if you can. Thank you