I'm new to the fish keeping world. Had a comet goldfish that I bought for my son for 30 cents for two years. He was outgrowing his 10 gallon tank so I upgraded to 20 gallon, stupidly without cycling the new tank.... he died two days later. So now with a brand new 20 gallon tank that I had successfully cycled I added 3 male guppies, 2 swordtails and 4 glofish tetras. The tetras died overnight. Went back to Petsmart, had water tested, it was fine. Waited two weeks, added 4 more glofish, 3 died within 2 days. I’ve since given up on the glo fish. May add a white skirt tetra for my one remaining glofish, but I digress! A lot, sorry Anyway, now more than a month into this with guppies and swordtails, the guppies have harassed the swordtails into flashing up and down the side of tank non stop and they haven’t eaten in 3 days. Tested water again, all within normal limits except it’s a little hard. Went and got 6 female guppies yesterday and added 2 female Dalmatian mollies in the hopes that the guppies would leave the swordtails alone and maybe the swordtails might be interested in the mollies, but not be able to mate and create an overflow of unwanted fry that I was sure the guppies would be providing. The guppies are totally uninterested in the females and continue to follow the swordtails up and down the side of tank. Everyone is acting fine and eating normally except the swordtails. The male guppies take breaks from the harassment, almost in shifts to eat and swim and then go right back to it. Not sure what else to do.