Filter Changes?

[jdesormeaux]

Hi All:

Quick question. I have a "hang on back" filter, one of the stupid ones
with the carbon inside of the cartridge that slips into the filter, and I
was wondering how often they need to be changed. I use to do it avidly every
second week but then noticed that at this time it's been 4 weeks no blockage
no measurable ammonia, no nitrites etc and my water is crystal clear,
however there is alot of goop on the filter cartages themselves.

So what do you guys think, to change or not to change that is the
question ;).

Thanks in Advance
Joey