Okay well first of all what kind of light are we talking about here? That's a pretty small space. Keep in mind given a natural environment this plant is very comfortable growing in excess of 2-3 meters tall. You're trying to grow 3 plants in less then 1/4 that size space (40cmx60cmx70cm = roughly 16"x24"x28"). Now I'm wondering here being such a small space you shouldn't be needing to use a very strong light so I'm kind of thinking the cool tube is overkill or you're trying to put too strong of a light in too small of a space but if so you wouldn't be thinking some plants aren't getting enough light. Another thing that's working against you is all the fans. What you describe first off is way more then a space that size should need. Your space translates to approximately 6 cubic feet. The maximum rate of air exchange for cooling one should use is enough to completely exchange the air 5 times per minute or in this case roughly 35cfm's I believe most 120mm fans are rated for at least 50cfm's so one 120mm fan should be enough but you got 4. Also what you describe is called an active intake/active exhaust set up. That's a design that only really works in large spaces. In small spaces you want to use a passive intake/active exhaust. If the space is well sealed except for the intake and exhaust then when the fan sucks air out the negative pressure created by the space that air occupied will naturally draw air in thru the intake. In a confined space the active intake actually works against the exhaust by adding positive pressure and so heat doesn't get ventilated as efficiently. So you should lose the fans on the intake.
For that size space your light should really be in the form of cfl's, at the most maybe a 250W HID. None of those, with proper ventilation, should need a cool tube.
Personally, if I had to grow in a space that small I'd only be flowering one plant not three. Not that it can't be done but it's alot of work keeping plants small and healthy and the yield hardly seems worth all the effort and risk. In the end one bigger plant in that space will yield about the same amount as three smaller ones will, maybe even a little more and it'll be alot easier to care for. The down side being you'll have no variety and if you're a heavy smoker you'll run out before your next harvest although that would be true no matter how many plants you had in there.
To answer your question though, you should be able to remove the cool tube although I'm not sure you need a hood that'll also eat up space. I think ultimately your problem is going to be keeping the plants from growing into the light. The cool tube helps protect them from that but at the same time reduces the room for growth. If I were you I'd be looking for some way to relocate my grow to at least a closet where I have more room to work with and therefore more options. Although that would probably mean buying stronger more powerful lights and fans as well as additional pots, soil, nutrients, etc.
maybe i will add another fan for exhause so i will have 5 for exhaust, 2 for intake and one 22cm for pushing hot air into exhause fans. I think i will give it a go and see what happens without cool tube. Another option is to flip cool tube and light in opposite direction of that direction in which is now, but i think it will not fit, because the sice of the box and because the hose for cool tube should be either attached to cool tube and it takes a little bit more space. A have one little hood for lights...a will maybe this one or do some modification on the cool tube hood, whitch is bigger and a think more efficent.
Seriously though, the things don't seem to work worth a damn. Now floramite surprises me because I thought I heard that stuff was good but maybe I'm confusing it with something else?
