I have a 55 gallon tank that I'll be posting in my aquarium log. But i had 7 Von Rio Tetra's and now i have 4. For the past 3 days, 1 has been dying everyday. It started when I put in my DragonFish from walmart (mistake) and it died the next day. But that day, 1 von rio died. Then the next day 1 other died. the so on. But today, I changed 10% of the water and noticed the von rio that nearly was about to die had a white area on his head. after the water change, he died. Had my water tested, and they said that my P.H was just a tad too high. All my other fish are ok. Im guessing that they not be as hardy toward P.H or what? any help appreciated. thank you.