I'm asking for advice or information for my husband and myself. My dear hubby recently got a new tank. He used to have a small tank when he was much younger (early teens). We now have a 55 gallon tank with a Penguin bio wheel filter. We set it up on June 18, let the filter go, added dechlorinating solution and a live bacteria solution. No fish on the first day. We bought 2 gold barbs, a molly, rainbow shark, and a Chinese algae eater on June 19. Everything went fine for 2 days, then a gold barb passed. The other barb lasted 2 more days. On this Sunday, 26th, we purchased and added 5 green tiger barbs and a bumblebee goby. The molly immediately began swimming around with the barbs. Nothing strange Monday. Early Tuesday morning (28) my husband found 1 of the new barbs dead and a second nearly dead. Later in the day we have seen the molly chase and nip the remaining barbs until they were dead. After removing the barbs, the molly swam around like normal for about 30 minutes, swam towards the top next to the heater and has remained there all evening. My husband tested the water today with a 5 in 1 strip. I don't know the values, but he said everything was in proper range except the PH which was high at 8.2. We added ph correcting solution. We attempted to vacuum and replace water with a python gravel vac this afternoon, but that was another problem on its own, and ended up replacing only a small amount of water. The molly has not nipped any of the remaining fish (rainbow shark, goby, and algae eater). Any information, advice, suggestions are needed and welcomed! Thank you in advance.