The K-9 is, I think, Colombo's only attempt at a comprehensive pet store. They sell a range of products for pets like cages, leashes, chew toys, shampoos and, strangely, adult diapers (?). You can purchase items for most house pets - birds, cats, hamsters, etc - but the shop seems better catered towards the eponymous canine.
The lady who was at the counter when we shopped for our first dog over eight years ago is still there and very little seems to have changed - including the prices. Unfortunately K-9 is still as expensive as it always was. A dog leash can cost upto Rs. 3000 and simple plastic feeding bowls are well over Rs. 1000 (most things in here are imported). There's probably a cheaper alternative to everything in here lying about somewhere in Pettah. The only hassle would be finding it.
However, K-9 does have some high quality products that might be worth the money. The feeding bowl that we bought our late labrador eight years ago is still being used by our dogs today, and they've got some elaborate chew toys which could be handy for distracting puppies with a penchant for footwear.
K-9 might also be helpful if you own a large dog - one that requires a good, sturdy leash and a large feeding bowl. They're expensive, but they're good quality and they last.
If you've got the money to spend, K-9 would be the convenient option for purchasing your pet paraphernalia. You won't have to go hunting around for all the things you need and the items are likely to be of good quality. But if you're looking for something like a feeding bowl for a little dog, a good option may be just to buy a tub of Elephant House ice cream; you get ice cream, puppy gets water bowl, wallet stays stable.
They don't sell food for cats or Pedigree, but you can get this at most big supermarkets. You can also purchase pet items at ODEL and Arpico for cheaper, apparently.