New to the site. Just got fish about 3 or 4 months ago. Right now we have an albino oscar and a regular black oscar. Both a little over 6 inches long. I am having problems with the pH in my tank. The 2 big oscars are fine nothing wrong with them at all, but anytime we get another one or we had 2 green spotted puffer fish they die within like 24 hours. I don't know if it's because there smaller or what. I bought a test kit and Nitrate is good, Chlorine is good. My pH is ranking at 8.4 and my alkalinity is at 300. What is the best thing to get it fixed I can't figure it out. Any help would be appreciated. Thanks!