Are your rats doing OK? Have you had any deaths in the colony or sickly looking rats? If you are getting your rats from another source besides breeding them I'd look into it, maybe find another source. I had a sickness run through my rat colony when I first started, I was throwing out dead rats every day. I finally figured out it was the pine bedding that was toxic and was giving them respiratory infections. I tried multiple antibiotics in the water and nothing helped, finally switched over to shredded paper and the problem went away.