i have a 3x3x6 indoor grow tent. got my temp managed to about 75-80 degrees. humidity is low, averages about 40%. do humidity packs work? seen them online. i have 2 humidifiers i got from the store and they seem to have no impact. trying an economical way cause funds are limited. thanks
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In every phase of vegetation or flowering Is required different humidity, in vegetative start high And in Finish od flowering low😉
I believe you are referring to vpd. @imSICKkid posted a nice chart for that! 
If you do a search for vpd charts, you’ll find it!
OH sorry Now i understand, sorry for bad advice 
Old post but something cheap I used to do was add a bowl of water below my air intake fan. It worked like a charm. Cant remember the how much it improved, but it did work for me. Might help someone.