Thanks for your replies everyone. I'm just so glad that I caught this in time so Storm didn't have a relapse. So far everyone is doing well and they all love the new food. The food also makes them drink more water and make a lot more pee biscuits so it helps to flush out their systems. The Waltham/Royal Canin S/O is safe to feed to healthy cats or else I wouldn't be feeding it to both Sunny and Sky. I'll update you when I can about Pepper.