Alright couple of answers in regards to some questions I have seen you post. I know I already gave you my typical copy and paste hello, but here it is again just for good measures:
WELCOME to RIU. You will find a lot of great information on here, but also some not so great information. The most important thing is to continue to learn and do individual research to find what works best for you in your garden. Make use of the forums search bar, as this is a great way to find threads that are posted on topics and questions you may have. Furthermore, don't take information as being a 100% valid without verification, I prefer members who have photos, videos, etc to back there claims, but even then every garden and grower are different.
Finally, please know that "Well-Known Member" doesn't necessarily equal "Great/Knowledgable Grower" as many new members tend to make this assumption. I am a prime example of a new grower, who has received this status simply because of my activity on the forum!
Best of lucky with all your grows and again welcome to the RIU community!
Alright, moving onto the question from previous post. As far as for a dresser grow, I personally would not use computer fans, but that is just my personal opinion. You can find fans that will move more air in and out of the unit for only a little more if not the same price.
In regards to the question at hand on this post as far as a DIY carbon filter, I have no experience with building one myself but by simple typing in "DIY filter" into the RIU search bar and selecting the option for "search titles only" you will come up with numerous threads on this exact topic.
By no means am I trying to come off as being rude, just trying to hopefully steer you in the right direction. As a new member to this forum myself if there is one thing I have learned about getting help from others, is that you must do some leg work first or they will not usually be willing to help. Best of luck on your grow, and again, welcome to RIU!