They, more than likely, have been eating that nasty store food with the corn, alfalfa and all of that mess. They can't digest it and it just passes on through. The store owner may have been feeding them watery lettuces, which also causes diarrhea.

I would stop using the Dri-Tail, never had a use for it and have never seen a case warranting it(maybe in hamsters, but yogurt works the same). I would say that it is probably nerves from a change in environment and the change in diet causing the diarrhea. Not much to worry about. You can always go get some pyrantel pamoate(Strongid) from your vet and give them a few drops. If they are wormy, that will take care of it. OR you can trek to a feed store and get a tube of 1.87% Ivermectin ONLY horse dewormer. The small tube that treats 1250lbs will cost you only $5 or so. Give them an uncooked grain of rice-sized dose once a day for a few days. That will get rid of most internal parasites safely, and you still will have tons left of the stuff

If you want to firm up their stools, give them some cooked brown rice, some oatmeal(old-fashioned slow cooking) and some yogurt(any flavor is fine). That will help, as will giving them a few days of quiet so they can settle down.

Hope that helped.