Question about carbon filter

So my question is i have a 6" ipower carbon scrubber with a 6" 530cfm fan (or so it claims) and only 4' of total ducting that 2' is a duct silencer. I am struggling with temps, it has been unseasonable cold here in the northeast and my room temps are 71 with lights on and 65 lights off, i put a speed control on 10% and still have negative pressure (crawl space grow box) so i hope that will help with that problem and ny filter problem.

Ok so my prefilter is weekly remove and beat all the dust out. I washed it yesterday without fabric softeners (if i recall they can clog breathable fabrics) and it is really pulling some air, i will occasionally get odors in the garage where it exhausts to. Could the fan be pulling too fast and not giving the scrubber enough time to do its job? The carbon filter doesnt state what the cfm rating is but their combo sell them with a high cfm fan, which i can assume isnt nearly as strong as a 530cfm fan. Since i added a speed control and now at 10% will it be better for odor scrubbing.
I dont care about the occassional odor but some people have noses like a bloodhound.

 

I double checked the duct between the filter and fan just now cause that also was my first thought. Since anything after the fan would have positive pressure and any leaks would just renter the grow room. Well i cant see any visible pinholes and when the fan cranks up it sucks the filter and fan together to where the flanges almost meet. I just threw a heater in there so ill have to watch temps. I have a heating pad to keep the floor warm and pot soil near 73. But i hope that speed control fixes the smell and dont have money for a new filter till after the holidays. I cant smell snything so that has me paranoid, if I've been out for awhile snd come home i can smell it if the prefilter needs shakin out. Im getting some ona gel pro and putting a spoonful in a solo cup in my garage. Only time will tell if it worked or not