a month ago i introduced 4 marbled hatchet fish to my community tank. one died a few days later but the others did marvolously well. they seemed to love my tank and would become very excited at feeding time so after three weeks i decided to get some more. last saturday i bought 6 more. in the last week all but one of the new fish have died, but so have my exsisting fish as well. up now ive lost 3 cardinals and 3 endlers. all at random times with no signs of disease. they can be fine in the morning and a few hours later dead. all the other inhabitents seem fine. active colourful and feeding. all my water perameters are good. amm 0 nitrate 0 nitrite 5. ive been keeping fish for a couple of years now and dealt with ich droppsy and most of the usual suspects but this is a real head scratcher. my tank is 125l planted set up and up last sat was my pride and joy. its really upsetting to keep finding dead fish. any help or advice would be most welcome. thanks folks.