check rotifers under microscope ?

[Myka]

You can also see rotifers fairly well using a Jeweler's Loupe which you should be able to find for $5-10. Also, dead rotifers sink when there is no water movement, so if you scoop out a shot glass from the culture and put it on the counter for 5 mins, if there are any alive you will see them in the water column as long as your eyes are decent (use reading glasses if you normally use them).