1 week after completing giardiasis treatment, showing symptoms again?

So on March 1st I finished treating my two lil guys with Metronidazole twice a day after a week. Poops were regular by the time the treatment was finished. Have cleaned the cage once every three days since the treatment was completed.

I'm scheduled to repeat the treatment starting March 22nd. But today, a few hours after cleaning the cage, I noticed that Dex (the one who tested positive for giardia in the first place) had runny stools that looked JUST like what I had seen pre-treatment.

What do I do? When it comes to diet/environment I've changed nothing. Should I go to a different vet and try to get a different medication? I've been super careful and I don't know why this is happening.

Giardia can be a bear to treat and it sometimes it doesn't get handled the first time. Also, giardia is a forever thing. A stressful situation can cause your chin to start up again. I don't think vets share that with people very often, so people think it's a one time thing and then it's gone. Sadly, it isn't.

You said you cleaned the cage. How did you clean it and what did you use to clean it with?