A 4x4x6’ is a great tent to start out with in the beginning .I do understand what you mean about cost it is a very expensive hobby when you first start out . The 400 watt light you have will work in a 4x4x6 tent but you will need to get an exhaust fan and a hood for your light . MH and HPS bulbs kick off a lot of heat this is another reason I like led lights. I would say the biggest draw back for led lights is the up front cost , but if you are seriously going to do this for a long period of time they will save you money in the long run in electric and bulb replacement and heat issues. I know there are a lot of grower’s in this forum who use the mars hydro led’s me I have 2 platinum p450’s that are equal to a 600 watt MH/HPS (that is each led light both together would be 1200 watts). Now because they are equal to a 600watt light dose not mean your pulling 600 watts out of the wall where as you are with a 600watt MH/HPS. Mine with just the veg switch on is pulling roughly 137 watts and with veg & bloom switch on it’s pulling 387 watts. So you can see I’m only using half of the power of a 600watt MH/HPS with the same results. When your running a bloom cycle of 12 on and 12 off you can run for 2 days with an led at the same cost of running a MH/HPS for one , over time the savings really add up. If you decide to get an led make sure it’s a full 12spectrum led with IR (infra red) and UV (ultra violet) lights.
got a 4x4x 72" tent today and a proper hood im well in my way got an air cooled hood local store had a steal on them so why not now for fans and filter any suggestions on a good cheap filter fan setup. You guys are literally walking me through the process of setting up for a successful grow and is much appreciated.
They have links in the section for affiliatesale, you’ll need a 6in to fit a hood I think the one on here is 130 for fan filter and speed control
Nug-bug is right check amazon for a fan with a speed controller there pretty reasonable. As far as a carbon filter I would not worry about yet not till you get to flowering that’s where the real funk starts. You will need ducting for your fan at what every size your hood intake and exhaust are be it 4" or 6" your ducting needs to be the same size as your fan and I’m sure the place where you got your hood would have the ducting. Setting up fan and ducting there are a couple of ways to do it . Near the top of the tent you should have one hole on each side of the tent run ducting out one of them and attach the other end of the ducting to your hood and at the other end of your hood attach the fan to the hood with a little ducting then a little more on the other end out the other side of the tent. Be sure to tape up all ducting connections with duct tape. Now you’ll need to get some fresh air into you tent take some of the ducting and at the bottom of your tent you should have a hole around the same size as what you had at the top bend the ducting in a upside down U put one side outside the tent the other in with openings facing down this will give you fresh air and block light during dark periods. Congrats on the tent & hood your on your way my friend. 
Amazon is a great resource
They have fan and charcoal filter set up for less than 200 and a speed controller for a couple 
More so I’d start there I bought my charcoal filter for under 40
The hood i got is sun systems sun grow air cooled 8in the plan is getting another ballast prob a 1000 watt dimmable hps/mh i want something that i can use the 400watt dimmable ballast i got now for seedlings and clones and then when they get big enough to put in the next tent, bump it up to using the 1000 watt dimmable ballast in my 4x4 tent since i got the 8 in cooling hood maybe start on 600 for veg and bump it up to the full thousand for flowering does this sound acceptable to all the OG growers out there am I on the right track? also is it better to put the carbon filter outside the tent and pull air inlet it push the smell out through the filter, I have seen and heard both ways work but what’s the most inconspicuous method at the end of the day that’s what really matters being discreet i got 1 4x4x70" tent in my room as of right now and got room for 1 more 4x4 and one smaller tent in the whole room the measurements of the whole room the tent is sitting in is 15 ft length x 12 ft width no windows in the room but can do what needs doing for vent and air into the room figured i would neck down the hood to 6 in as the stuff on the tent is 6 in and the kit your talking about fan filter on amazon sounds like just what i need to do what i want once again thanks to the whole community you have definitely brought me out of the stone age in a matter of days this is the best community ever all the things i love in one place marijuana and a community around it lol thx again guys…and gals…
@xxpain4uxx enjoying learning along with you. I’m having a little trouble visualizing what @tee3737 is describing. I’m getting ready to start my first indoor grow and I’m reading all the forums and learning a ton of good info here. Lot’s of good folks willing to help out is a huge plus.
Hey Bob31. I’m also a 1st time indoor grower. Got a headache with all the stuff you need to learn. I have a small growing area and a 1000w LED light. Is that too much lighting? Disparate need of help.
Hey @bob31 what are you having problems with visualizing I’ll see if I can put it another way so you can. Welcome to the forum. 
Well, my head is sort of in information overload and I have read a bunch of posts and such about ventilation and like everything else they are lots of different ideas as to how it’s done, but very few offer drawings or enough pics to really make it clear for us truly FNG’s who don’t have a clue… So please understand, it’s not your explanation only my comprehension.
Hey @Rdg1951 Maybe we should do a co-post on our “issues” and let these guys get back to helping out @xxpain4uxx ? What ya think?
No problem @bob31 all info can be a little hard to grasp with out visual aid I get that bro. Utube has some videos on setting up grow rooms. I like a guy called The Grow Boss check him out.
Will do, I hadn’t thought of youtube but I’ve seen guys recommend that in other posts. I’m off to watch some vids.
I was just wondering if the LED lights I have are too strong for a small
area. It’s a 1000w. I think I have the ventilation system worked out. Just
an old Nam vet trying to grow enough for me.
I’m only gonna grow a couple plants to start so I’m going with a small 300w LED Light. More of an economics issue as start up costs can be a bit staggering if you’re on a fixed income. I’m a little younger, but not by much. I went in the Army in '78.
my growing area is very small so 300 is all I need right now. By this time next year I will probably have a few more.
I was in Nam 69–70. I really appreciate the input. Yes I am on a fixed income and can’t afford what they’re asking. I wished I would have done this year’s ago.
Thank you for your service.
That a great idea @bob31 that way where not stepping all over @xxpain4uxx thread. Do you know how to fill out a support ticket.
Sure I saw it at the top of the forum. I will get one started
Rule of thumb 50 watts per square foot I believe for two plants
Wow 50w per square foot… Holy crap I’m going to have to knock out a wall. I’m talking about a 3ftx6ft. 7ft high.