Smelly, kinda mushy stool- food problem?

Hullo all!
I know that this topic was addressed rather recently in chris32799's post about his Bengal
here
But I didn't want to hijack it for my kitten

Since I've had her (she is almost 5.5 months) she always seems to be having slight stool issues. It seemed to have cleared up, and I slowly switched her over to the food I was feeding her (Innova Evo). The other day, however, as I was cleaning the litter box she saw fit to use it and I saw that the stool was kinda runny and loose.
I immediately switched her back to the Science Diet ID food, and now she seems to be a bit better. Her poo has a good shape and looks alright, but is still really soft and gets all mushed up when she covers it.

Is this normal?

I also picked up some other food to try and switch her over too, I thought that maybe the other food was too rich for her, could this also be a problem?
The woman at the pet store said that some owners do have issues with the more holistic diets, and that mixing it with some corn syrup or other more grain based food seems to help.

My vet does know about this and has done 3 fecal tests...all with negative results.

I would very much like to try and settle her stomach and clear this situation up.
Any ideas would be welcome!

Thanks!

I dub Evo a 50/50 food since about 50% of cats cant handle it being so rich...

why was kitty on I/D and did the vet okay trying Evo ...??? How slow did you switch and are you using canned or dry or both??

Has the vet tested for this tri trichomonas foetus ??

Wow, thanks for the fast response!

The vet had me put her on an ID food when I first got her and told her about the diarrhea issue (around 8 weeks).
The vet had recommended the Science Diet Kitty formula, but I decided to go for the Evo instead.
The food I just picked up to try Georgia on is the SD kitty formula.

I took over 3 weeks before I had completely switched her over to the Evo food, and she seemed ok.

I don't know about that specific test, but I can call them and ask about it.

Thanks!

okay ... IMHO SD is way over priced for what you get ( the regular stuff no the rxs )... would you like maybe some suggestions for simple yet quality foods??

I don't mind the price... but if you've got anything else in mind that is a healthy food that maybe isn't as rich as the Evo I'd love to hear it!

thanks a bunch Sharky!

Taste of the wild is a $$ reasonable yet grain free I use ...

Simplier foods

Natural choice

Califonia natural

sensible choice

Thanks!
I'll see if I can find any of those in my area!