Semi-clear Gel

[epl4978]

In one of my tanks a semi-clear gel has started growing. it has killed most of my fish in the past two days i have no hospital(sp) tanks to put the other fish in. What is this gel and how do i kill it. it is growing on a amazon sword and on a piece of drift wood also on other parts of the tank. it appeared after a sword tailed died when i was away from home and i can home(with in a couple hours) and the fish was covered in this gel and stunk. i did a water change because my other fish were all hovering around the bottom and that solved the problem for a couple days and now most of my fish are dead.

thanks for any help

Evan

 

[WILDER]

Sorry need more info on size of tank in gallons, how many fish and which type plus water stats in ammonia,nitrite,nitrate,and ph, what colour is the gel, is it slimey on the fish and excess mucas on the gills or laboured breathing.