Potty Problems X2

So I'm pretty sure my two little ones are finally getting along. I say pretty sure, because they still fight with each other, but there's also moments when they groom each other and I have even caught them snoozing together a few times! But anyway, we seem to be having a different problem. They both have developed pretty loose stools. Ruby has been having this problem for awhile and since bringing Nova in, she seems to have slowly followed suit. I thought it was a sensitivity to fish on Ruby's part, but what are the chances that both of my cats are both experiencing the same reaction? I'm on here to ask you fine folks because I had brought it up to Ruby's vet before we even picked up Nova. She said that most likely in a kitten coming from the SPCA it would be worms. However, she was dewormed by the SPCA and the loose stools started weeks after we brought her home, prompting me to think it was something that happened to her within our home environment and not something she picked up while at the SPCA for 2 days (we picked her out as a kitten at her foster home and went to get her right after her spaying). My suspicion is something along the lines of food related still, but I just don't know anymore now that my second cat has begun to have the same symptom. They both were on dry food only when we got them so there is the switch to wet food to think about. But it's been about a month that we've had Nova now so I wouldn't think it would last that long if it was just the transition causing it. I have tried a lot of different brands of food because Ruby is pretty picky, but I'll rattle off what I can remember. I believe we started on Blue Wilderness, briefly tried Nutro Max and Royal Canin, Wellness (which I'm pretty sure is when the loose stools began), then Nature's Variety Instinct and now we are onto Weruva, but I also know they both like Tiki Cat as well. I have recently cut out all the varieties with fish, so they are only eating Fowl Ball and Chicken Frick-a-zee. I'm looking for any possible explanations any of you can think of in reading this. Please let me know if you need anymore information. And thanks in advance!

~CheshireKitty, Ruby, & Nova =^.^=

There is a PCR stool test that can be done.  It will test for parasites and bacteria overgrowth that the float test done in the vets office doen't test for.   I think with the second kitty now also having issues that it could well be some type of parasite.

Thank you for your reply. Where or how would I do this?

The vet would send the sample for you.  It's best to get the sample while he is having diarrhea.