DIY Carbon Filter Question

[alext512]

Hey all- I've got everything assembled to make a small DIY filter for my small first time grow except for the carbon. I've read in a few places that we want to be using carbon specifically for air (as opposed to water/fluids). But everyone suggests getting the carbon from the pet store, which is for aquarium tanks (presumably for water).

Does anyone have an explanation for this? Essentially, I just want to make sure I buy the right carbon for our use. Thanks!