help tank is dying off

well came home from work all the fish are dead.. only inverts and a chainlink eel are alive

hes going into qt with fresh h2o reactor will be up and running sat with carbon... the carbon i have is currently running in a hob filter

 

well i went ahead with the water change, an almost full water change and siphoned the sand out. we took all the rocks out and found 2 with goo in afew crevices, im thinking this may be the remains of the missing nem. those 2 rocks are being boiled and boiled and boiled some more. then they will be bleached let dry boiled afew more times. let dry in the sun and boiled again in RO water, then my last thing im going to do is put the 2 rocks in a 5 gallon tank with a carbon reactor in it with fresh ro water and let it run for a week or so.... what do you guys think ? i also added a carbon reactor to the tank as well as dosed bacteria a little more then double dose ( DR. Tims)