I only had 5 of them going, but after the first two and a half weeks they started smelling. It was an overnight thing, there was no odor and then "bam" it was there and noticeable. I used Ona Gel which worked great. However, they definitely put out a noticeable odor. It wasn't super potent like skunk or anything but it was noticeable enough to get you busted if you don't use a carbon scrubber or Ona Gel. When I first started growing them I was going to do it without anything to treat the air, but after the first few weeks I quickly changed my mind and had some Ona Gel shipped overnight. So, yes, please do yourself a favor and get a carbon scrubber or some Ona Gel. The Ona Gel only lasts for about 6 weeks so you'll want to buy 2-3 of them if you go that route. Next time, I'm just going to go with a carbon scrubber though. Goodluck.