Throwing up - when to be concerned

We adopted Leo and Clarkson in the beginning of August at 12 weeks. I guess that makes them over 5 months old now. Leo is our first ever sensitive-tummy kitty. When we first brought them home, he had the most trouble transitioning to the new wet food and was frequently throwing up. Now that he's used to the new food, he throws up less, but he still does sometimes. He's a tiny little thing, but he eats with great vigor and we suspect that he throws up because he eats either too much or too fast. It's usually barely digested food - one time I came home from work and found what looked like a whole fresh can of cat food on my carpet. Really, it looked like someone opened a can and just dumped it there. Since I know that didn't happen - my bet is on Leo! 

The problem starts here...yesterday afternoon, he threw up a TON of brown liquid on the kitchen floor. I know it was him because I was doing dishes at the time and witnessed the whole nasty thing. It was really a LOT of throw up and it was pretty much all liquid, just a few tiny specs of undigested food in there. Then just now, maybe 36 hours later, I found a very similar looking puddle of brown liquid on the kitchen floor. I didn't see who did it, but it was definitely either Leo or his brother. He's still eating normally and acting just like normal, but I'm kind of alarmed at the amount of stuff that's come out of him in the last 2 days! I haven't been able to spot him in the litter box yet, so I can't say if he's pooping normally, but I didn't see anything abnormal in there anyhow. What could cause this and when should I be concerned enough to see a vet?

The first part isn't too worrying. Some cats take a Long time to transition to a new food, and even then if they eat too fast, they puke. There are many techniques for slowing them down: smooshing the food on the bottom of the plate(wet), watering it down (wet), putting a rock or golf ball in the bowl so they have to eat around it (dry), putting most of their meal in a treat dispenser (dry), raising the bowl or simply putting only a spoonful at a time on the plate.

The second part is more worrying... I have no idea what all that brown liquid could be, but since it was already digested, I think it unrelated to the first issue. I would see a vet about that. :nod:

the undigested food probably isn't vomit. my cat zala appeared to be vomiting but actually, the so-called "vomit" was regurgitation, which is healthier for cats than vomiting if it appears to be on a regular basis. the brown liquid, however- SEE A VET. that could be really serious. what shade of brown?

From-memory,my-vet-said,if-the-throw-up-is-immediate-after-eating,and-whole,the-issue-is-in-the-e-sof-a-gus,if-its-later,and-the-food-is-digested,hence-the-brown-liquid,the-issue-is-in-the-tummy-or-intestines,as-in,a-blockage-or-IBD-or-what-you-are-feeding,does-not-agree-with-kitty's-tummy.

What-are-you-feeding?

In-any-case,you-need-to-take-the-kitten-to-a-vet-and-ask-for-an-x-ray.