carbon filter, how long to use before changing?

[stinkyattic]

You need someone to do a smell test..

Grey's not kidding on this one. If you live with your plants, you won't be able to smell it as early as someone who doesn't inhabit a house redolent of a skunk orgy... That's the only way to tell when it's change time. There are so many variables in filter life- mass of activated carbon in the filter, particle size, how it is packed, temperature, air speed through filter, how stanky is your strain, etc.