Problem with culture	Possible remedy	Possible prevention
Culture is overwhelmed by rotifers or other large organisms.	Remove as many Stentor as possible into a new culture dish. Then wash the cells three times.	Wash Stentor thoroughly when receiving them, even when purchasing them from a commercial supplier.
Culture is overwhelmed by fungus or other small organisms.	Identify a corner where there are the least Stentor. In that area, remove as much media as possible without removing many Stentor and add in new PSW. Mix gently but throughly to distrubute the invading organisms. Skip the next feeding and the Stentor will eat them.	Observe the culture regularly and remove small contaminants by exchanging media for fresh PSW.
Stentor are laying on top of each other.	Split the culture so that the concentration is less than 20 cells/mL.	Split cultures more often.
Stentor cells are mating.	Feed every 4 days instead of every 5 days.
Culture has a lot of dark waste material.	Remove as much of the dark material, Stentor waste, as possible without removing the cells. If Stentor are attached to the dark material, pipette up and down to release the Stentor cells from their waste and then remove the media with the waste without removing the cells. Or, remove those Stentor and feed accordingly less.	Feed Stentor 1 mL less food per 100 mL of culture.
Unhealthy-looking (vacuolated/bloated or rounded) Stentor.	Remove as much media as possible without removing many Stentor cells and add new PSW.	Exchange the media regularly.