How can I reduce the heat in my 5x5 tent (650w light bar/6" ac Infinity and a ton of fans) without AC? Do I have to leave tent open?

Do you notice the sides of the tent sucking in at all? You want it to suck in but not hard. If it's not hot air is most likely building up. You can try closing a flap and see if it helps your temps drop some. 🤘😤

Yes, just the passive from the vents (maybe 5"x12" on both sides). I should add the ambient RH here is about 38% all winter, so I run a humidifier to keep the tent at 50 or 60% during veg.

I vent it through the Tbar ceiling into another part of the basement. The lung room its in is staying at 68f or 20c.

I mean I have a mobile AC unit, but would I rather not use that, for multiple reasons. I can't really pipe in cold air during the day for my tent because ill forget something and kill them all. I just feel like im missing something or not using my fan/filter properly...or is it impossible to run a 5x5 @ 650w without AC?

Does your tent vent into the same room it's in? If so vent it into another room or space if possible. An active intake can help push in more cool air also. Or run a window ac unit if you have that option also. 🤘😤