Petey's tummy

He could have giardia, which doesn't show up on a normal fecal test and makes the poop runny and smelly. Could be coccidia as well, with the same problem of not being tested for in a standard fecal.

We experienced the same with Calvin. He had smelly, soft poop and he ended up having medicines to treat worms, which did not help a whole lot. We later figured that it was food related and he doesnot do well on richer kibbles. Moving him to a totally wet diet saw dramatic improvement. You may want to figure out if this can be food related.
Hope this solves soon!

How old is Petey and where did he come from? Did he come from a place with many other cats and not the best hygiene?

Soft, smelly poop is not normal and you have to get to the bottom of it. As mentioned there could be a lot of causes from chronic illness to food issues. What does he eat? A fecal is a good test to catch some things but it doesn't catch everything. When they do a fecal they only test a small sample and your cat can have all sorts of stuff that just isn't present in that one little sample. I would recommend repeating the test. There are also two types of fecal tests, a floatation and another that I can't think of the name of but it's more in depth and can catch things a floatation can't. You may want to find out what test your vet did. The floatation test is the most common. I'd ask to have the other one done if it hasn't been done already.

It's odd that your vet requires another exam in order to do another fecal. Usually it's okay to just bring in a stool sample and have them run it. Maybe you could contact another vet to see if they are willing to do that without actually seeing the cat. That would save you some money.
As mentioned giardia is hard to see on a fecal test so that could be it. Mushy, smelly stool is a common symptom of giardia. Giardia is spread by drinking stale water. It can be tricky to treat but it is treatable even though it may take a while. There are special tests for giardia but I don't know how good they are.

Another strong possibility is diet. Some cats just have sensitive stomachs or has allergies. If nothing can be found wrong with Petey that is a strong possibility. Of course it doesn't cost you any extra to check and see if another diet would help. Natural Balance has a limited ingredient diet that can be good for cats with allergies or intolerance to some foods. Since it only has a few ingredients it's easier to pinpoint what is actually causing the problem. It's not the tasiest food so you may want to start with getting a small bag in case Petey refuses to eat it. There are many other foods you can try. I would also mix in some probiotics in his food. 8 days may not be enough to see results, especially if he doesn't tolerate his food so just because it didn't help before doesn't mean that it won't help now. If Petey is put on medication for his problem it's very important to use probiatics during the treatment, especially if he's getting an antibiotic like metronidazole which is a common treatment for diarrhea.
I'm a bit surprised that your vet didn't suggest any kind of treatment. It certainly wouldn't hurt to put him on 10 days of metronidazole to see if it works.

Anyway, to make a long story short, I would change his diet and put him back on probiotics (you can buy Fortiflora and other probiotics online) and if you see no changes after a couple of weeks or so take him back to the vet. It may also be a good idea to deworm him (with pyrantel pamoate) to be on the safe side. It doesn't hurt.

Good luck!

This sounds EXACTLY like what we've been going through with Calvin. We are currently trying California Natural because it has limited ingredients, but you seem to have already done that. Perhaps grain-free dry? The way I figured out that it was the dry was by stopping it altogether and feeding only wet to Calvin and things cleared up. That may be something you can try. Then if you see that the dry food is the issue, you can experiment with various brands and see what suits you. He, too, had 2 fecal analyses with all negatives and 1 course of metro and 1 course of panacur.

If you want, I can meet you somewhere and give you some DiaGel... It has been a MIRACLE for Bugsy, pretty much taking care of his diarrhea that he had for 4 months, when nothing else worked! It worked wonders for Bluerexandbear too... As you know, I am in Dallas... It is costly, $12 each, But I will be happy to give you 2 of them - it is all you will need if it works PM me

I do not give strictly grain free wet to my kitties. But the only "grain" they get is rice (not brewer's rice). I have heard about the UTI issue (or is it blockage?) but not too sure. Calvin did not tolerate any grain free dry food so far, so if California Natural is something he tolerates, it will not be grainfree. Plus they only get between 1/8 and 1/4 cup dry. As for wet food, I have wellness grain frees, Fancy Feast fish and shrimp (I think grain free), a couple of merrick's (grain free) and a Trader Joe's (has rice) in circulation. I am very new at this and still learning but I know there are many, and Sharky especially, who know a lot about nutrition. 1 once read in some thread that someone said that feeding the worst of the wets is better than the best of the dry kibbles. I would avoid any wets with wheat gluten, corn, soy, brewer's rice and by products (meals are fine, as far as I understand).
We did give Calvin fortiflora but that did not help at all.

I, too, have heard about UTI and grain-free and am worried about that. But I finally found a food that Pipsqueak can have normal hard poops on, and that is Wellness Core. I feed all my cats about 3/4 quarters wet (varieties, Wellness, Fancy Feast Fish/Shrimp, Evo, Solid Gold) and 1/4 quarter of the Wellness Core Dry. All of my cats have very normal poops and I have never found a cat food before that worked this well in the poop department.

I just know that it is not normal to have stinky, soft poops and you have to find out what diet works for your cat. I bet with your kitty, it is diet related.

It sounds like you're onto something! I'd keep feeding canned only and eliminate the dry and see what happens over the next several days. Then, you could try reintroducing the dry and see if you get the runny poops.