I have just added 15 cardinal tetras to my tank . The tank was looking cloudy so I added some seachem clarity the day after I lost 4 ! All my levels are good 0, ph is 6.8 The remaining fish are feeding and swimming when I looked at the ones that had died one had no rear tail fin , one had a whole under its chin another had the left fin missing !! Remaining tetras seem a little blotchy on the red coloration (front end).