My DIY carbon filter ain't working

I'm about 6 weeks into flowering 6 stinky plants and I've gotten a couple comments from people that can smell something funky. I'm so used to the smell I barely smell anything.

So I built myself a carbon scrubber from this tutorial: http://icmag.com/ic/showthread.php?t=31679&highlight=diy+carbon

My fan is a 105 CFM centrifugal inline 4". I'm using a 4" core and a 5" shell so I've only got 1/2" carbon layer. My filter is also 2 feet long. It worked great for the first day or two but I've been informed the smell is returning.

I'm pushing air into the filter because I don't have room to put the filter inside my small rubbermaid setup. When I put my hand over the filter to feel where the air is coming out it seems to be strongest at the end furthest away from where the air enters. It's like the air just blows through the filter hits the end and then decides to mostly exit near the end.

I'm wondering if maybe my carbon scrubber is too long for my small fan since the air seems to be mostly escaping towards one end. I was thinking building an over-sized filter would be better to prevent the air flow from being restricted too much but maybe it would push air out more evenly with a smaller filter? Anyone out there successfully getting away with using 1/2" layer of carbon?

I'm no expert, but I think the problem comes from pushing rather than pulling air through the filter. I built pretty much that same filter for my cabinet, although only about half as long, and it works fine with up to 8 large, flowering plants. I can feel air being sucked through my filter pretty evenly along its entire length.

I also think a filter that size for a Rubbermaid grow is overkill. You could probably get away with the same basic design, but much smaller. Something you could put inside or even (concealed) on top of your tubs. Something that would enable you to pull air through it.

Just curious, how do you fit six plants in that little tub? You must keep them very small.

whether pushing or pulling, the air will follow the least resistance. try taping a plastic bag over the end, to force the air out through the rest. having even flow throughout the carbon is key. it's like trying to catch fish with a big whole in your net.

Looks like you did a pretty good job on the scrubber. .5" doesn't leave much room for error, especially on big ones. Once you're certain the joints are air tight, it's a matter of packing the carbon so there's a uniform .5" throughout. It's pretty tough getting that stuff packed tight enough. Once you handle it a little, gaps start to appear and this is where the stink escapes. High humidity won't help either.

Big filter, little fan, and pushing. You have settling and a poor design, you can tape over where it has settled and force the air through the carbon, but not well, your fan is fine, if your design worked. Take a look at my scrubber in the diy linkorama.
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with a filter that big and in the open, u might as well just take the plant out of the rubbermaid.

I also do a 1/2 inch bed and it's working great for me (4" inner core-5" outer core)

You've shown us nothing concerning your actual ventilation system. Other than the open tub (I can't believe it runs that way) I see no evidence of intake, exhaust or fan. Show us what you've got.

FreezerBoy, glad to hear you're using 1/2" and it's working for you. I'll snap a couple shots of my ventilation tonight. Basically I got a 105 cfm centrifugal inline fan right above the open box pictured. There is a 4" hole right above the light and it pulls air up through maybe 6" to 7" of ducting and then pushed through my scrubber. By the way the scrubber is two feet long. The intake is passive and is way at the bottom back side, it's about 10" long and 2" wide. There is also a 30cfm pc fan blowing directly at the bulb. Temps are in the low 80's maybe around 82ish. Humidity is brutal it's in a damp basement with humidity reaching 80% to 90% with lights off. Lights on humidity drops to about 65% to 70% sometimes less.

I put plastic wrap around the half of the filter where the air was blowing out the most forcing more air to come out the end closer to where the ducting meets the scrubber. So far I haven't gotten any comments. I really wanna get my carbon scrubber working 100% before I move. Odor isn't too much of a security issue here if a little smell creeps out but that won't be the case in my next place.

Thanks for all the comments and suggestions.

Ipsissimus has it spot on.
Filters, especially DIY filters, can have areas that are not consistent for what ever reason. Maybe the carbon has fallen away from one area and created a gap. That one gap would be the path of least resistance and the majority of the air is going to try to escape from that one little area.

It may pay to take the filter apart and try to pack it better. Vibrating the carbon during fill is the best method, if you have a way to get that done. Bang and shake a little at a time until filled if not.