Increase my intake until it can equalize? So how do I do that? Do I have to buy another fan for my intake? If not, what is a good way to do reduce some of the negative pressure or is that not a big deal? And how can I tell if I am happy with the air circulation? Sorry for all the questions I am just new to this and want to make sure I am doing this right.
I have the same fan and same size tent, and I have been using it all summer, so maybe I can help.
I have two tents, a 2x4 veg tent and a 4x4 flower tent. The 2x4 has AC Infinity 4" intake and 4" exhaust fans (no filters), the 4x4 has AC Infinity 6" exhaust with carbon filter, and 4" intake. I also use 2 small fans inside each tent on low. For lights, I run the SF-2000 in veg tent and the HLG-550V2 R-Spec in flower.
I run my flower tent lights on 10 pm to 10 am, taking advantage of the overnight lower temperatures here in Vermont. I run the veg tent from 10 pm to 4 pm. I have found the best way to regulate temperature is to regulate the room first, because that is where you get most of your passive air intake. I have a big box fan in the window (this is a spare bedroom with one window on the second floor) on a temperature switch, the fan blows into the room cool air from outside, and kicks on whenever the room temp is above 72 degrees. I then have the flower tent exhaust fan running 24/7 on speed 5, this keeps plenty of air moving thru the tent whether or not I have the intake fan running. I then set the intake fan to 80 degrees, so if the tent goes above 80 degrees the intake fan kicks on bringing cold air direct from outside (thru a dryer vent in the wall) into the tent. This will go on and off as needed.
During the day, when it gets up to about 85 degrees outside, I reverse the window fan in the morning so it exhausts air out of the room. I turn off the intake fans for the tents since I don't want to bring hot air from outside into the tent during the day. With the lights off on the flower tent, I can keep the temps below 82 degrees pretty much all day, hotter than I would like but that is only on the hottest days. If I lived anywhere that got hotter, I would need air conditioning. Most days, the tent with lights of stays between 72 and 78 degrees.
That is what I do during the hot summer months. Once the temps start getting colder at night, I can get the room down to 65 degrees with the window fan, and then the passive air intake is plenty to keep the tents below 80 degrees all night and the intake fan hardly works at all. As the weather gets colder, I will close the window and regulate the room temp with fans thru the vent holes. I have a propane heater in the room which keeps the room at 70 degrees all winter. When it is that cold, I exhaust both tents directly into the room, and then exhaust the room as needed thru the vent holes in the wall.
Now, for your situation, the T6 fan is really too big for this size tent unless you are using the carbon filter, and even then it is really strong. In my 4x4 tent with the T6 fan on and no carbon filter, I couldn't put the fan over setting 3 without the tent almost wanting to collapse from negative pressure. It is really strong! You need to open all the port holes on the tent and install either 4" or 6" duct into each port hole, with 180 degree bends. Use 6 to 8 feet long pieces so they hang about 4' inside and outside the tent, this is to prevent any potential light from entering the tent thru the ductwork (unless you put HEPA filters on each intake). You need this to allow passive air to enter your tent as the T6 is pulling air out of the tent. The filters will cut down the air being pulled into the tent, so you will have to adjust for what works for you.
Now, even with all ducts open, I have my carbon filter in the tent on the T6 and I still cannot get the fan over 6 without the tent being sucked in pretty hard, unless I am running the intake fan at the same time. I typically keep the exhaust fan on 5 in the summer and down to 2 or 3 in the winter. To allow more air flow without sucking in the tent so much, you need to add a T4 fan onto one of your intake ports. Actually, you can get the S4 and run it on the T6 controller, this will keep intake and exhaust flowing and maintain negative pressure.
Based on the math, a 6" fan is double the CFM of a 4" fan, and with a carbon filter on the 6" fan should be reduced by at least 25%. Well, I have experimented with 2 - 4" fans both on exhaust with no carbon filter, and they did not come close to the negative pressure of one 6" fan with a carbon filter. So a 6" fan with carbon filter combined with a 4" intake fan will still have plenty of negative pressure.
With the temperature of your basement at 75-79 degrees, I think you will struggle to maintain 80 degrees in your tent with the lights on. You need to get fresh air from outside, especially at night, or air conditioning. Fresh air is ideal, for maximum CO2.
That is about all I can think of for now. Just remember, the more air you move thru the tent, the happier the plants will be, generally speaking.
