I have the same setup for my 4x4 6" and a 67 controller I have two 6" rexial fans one on each side with a stainless defuser to flatten the air so it's not just blowing on the pot in front of the hole. I do wish the fans would work with the 67 but I just keep them on low-half . I ran just the exhaust fan for awhile but I thought the tent was going to collapse lol so I added a single rexial then added a second one for more even flow
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