Gave in to the smell

[rhodes_96]

What do you mean by prefilter?

I don't put anything else in the baskets other than matrix and 1 bag of carbon on the top. I depend on the 6 sponges for mechnical filtration.

I don't think carbon is really bad for my tank since im not going with live plants in it. I'll replace the carbon once per month (or until the stink comes back which indicate my carbon is exhausted).

By not prefiltering the matrix in the basket you most likely clogging the media ! Those outer sponges are not designed for finer filtration. Matrix relies on it's fine pore structure to house bb. You may have enough area still left on the bio media for some bb to look after your system, but I am betting that the bad smell is coming from the majority of the media is clogged.

To fix this I recomend changing the top most basket with bio media with fresh clean media. Leave the other basket of dirty media until next service then change that one with clean media. Get rid of the carbon and replace the top basket with bio media. Use the blue filter pad for the fx5 on top of the bio media in the top basket. Allow 3/4" from the top of the basket down for the pad to fit. Do your regular water changes as neccessary. Once the last of old media is gone and repalced you should notice a big reduction in the bad smell, plus better water quality due to the finer filtration.

 

[aclockworkorange]

You don't ever need to replace bio media (maybe after YEARS you could). If it gets dirty you can just clean it. I also don't run any additional filter pads in my FX5 (that's what you're talking about, right?).
I really think the smell is not due to improper filter maintenance.