fd2f0995_rbil_Care___Is_My_Gerbil_Sick___My_Gerbil___
[It might be...] unless you have recently given him or her a lot of unusual foods or veggies, diarrhea is a serious symptom which could affect your own health (more...). See the vet. If you cannot see the vet immediately, start emergency ornicycline treatment. You might want to provide a warm corner with a heat lamp or reptile heater for comfort. Heat only one part of the tank so s/he can choose a comfy spot. Wash hands thoroughly after handling the gerbil, its bedding or anything in/around the tank, including the lid. If you have more than one tank, isolate the tank with the sick gerbil from the other tanks, but do not remove his/her cagemates until after you talk with the vet. (They may need treatment too.) [My Gerbil...] 
has diarrhea
Shawsheen River Gerbils - MA & CT - Gerbil Care - Is My Gerbil Sick?
My Gerbil...