I have had my 2 betta fish in separate 2 gallon tanks for roughly a year. With knowing that is not a good living environment i purchased a 10 gallon tank with a divider. I set it up with a heater, filter, and accessories. I then filled it up with water and conditioner then let it ran for roughly 3 hours to start cycling. I put both fish in (on separate sides of the divider) and they seemed to love it but when i woke up this morning one of them had sadly passed. I believe its due to shock since i didn’t correctly acclimate them to the new water but one of them is still alive and i don’t know what to do to ensure it doesn’t die. I know that they were used to different water conditions and with living in filtered water it has shocked them. What can i do to help?? or if i purchase new fish to make sure they don’t die by my now learned mistakes??