i have some fresh dts and they dont smell bad at all....
try subculturing it.... into a new jar.
fresh seawater to 1.020 into a pop bottle put a few caps full of the DT into it and put it under a bright light at about 26 degrees C. with an air stone bubbling in it
in a few days it should turn bright green if theres any live phytoplankton in it
i put a tinny bit (like a toothpick scoop per liter) of water soluble general purpouse plant fertilizer in the watter.
once it turns bright green you can store it in a fridge for a few weeks
you can always check if there alive under a microscope you can see them budding and reproducing.
