Pet Chemicals

I was at a store a few days ago and while wandering through the aisles in search of the right section I noticed a sign: Pet Chemicals. I think this was for fish or such. But it struck me as amusing as I pondered what a pet chemical might be, and who might have what.

Would you have a pet chemical? What would it be? Something simple, such as an element, like iron or aluminum, or a common compound, such as water or salt (sodium chloride)? Maybe something just a bit different, but not too much so, like potassium chloride? Something a bit more reactive, such as sodium hydroxide? Or something rather exotic, possibly with a bunch of benzene rings?