[GpsFrontier]

a mercury thermometer should be OK. 80 degrees should be OK for the air temp.

it was $170CAD plus shipping. already bought and in use so i wont be getting rid of it. it is 172cfm and i havent seen anything that powerful in this size at any home improvement store.

That would be way to expensive for me to consider. The portable box fan in my room that I use at night would be more CFM than that I am sure, and it only cost $20. Of coarse you would need to adapt it for the situation but that's no problem for me. There are plenty other options also like a simple bathroom vent fan I quickly found online. This one puts out 70 CFM and is only $19.95. Home depot and Lowe's have dozens of them to choose from. Not to mention all the portable blower and box fans to choose from. If you used this exact bathroom vent fan and used 3 of them, it would only cost $60 and give you 210 CFM total. These bathroom vent fans come in all sizes, shapes and CFM's and work perfect for cabinet growing structures. But don't worry you already have a fan.

i think the water is getting warm because the buckets are black

If the ambient air temp is 80 degrees in that confined space I am guessing that the water temp will be about the same, maybe higher depending on how much the buckets absorb from the light. I wouldn't disturb the plants to paint them but if you could cover them with something. I would use silver bubble wrap insulation.

i would need to keep the whole setup within the tent as there is no room in my house for this (my parents would kill me) and i cannot move it outside (they will kill me again). the air temp of where the reservoir is stored is 27C, the same temp as where i measured the temp at plant/bucket level.

Its kind of hard to tell how you are running the delivery and recovery of the nutrients from the picture. I am not sure if each bucket is its own reservoir or you have a single one for all the plants that doesn't seem to appear in the picture. You seem to have a lot of limitations and I don't know how many gallons of solution you need to cool down. Funny thing about that is you would think the less to cool down the better but that is not exactly the case. Yes it will cool down faster but on the other side it will warm up faster also. By the looks of the buckets I am guessing you have about 5-15 gallons of nutrients.

Because the nutrients need to remain inside the tent and from the picture I don't think you can use geothermal energy because you said it is not inside but it's not outside ether, so I assume there is some sort of floor. Assuming you have a single reservoir feeding all 4 plants I would try to generate your own geothermal energy. I would use a inexpensive Styrofoam ice chest (thicker is better). Get a copper coil splice it into the line you run from the pump to the plants. Set the copper coil into the Styrofoam chest, then fill the chest with Ice water. That way when the pump turns on, it pumps the nutrients through the coils submerges in the ice water cooling it down before it reaches the plants. You will probably need to change the ice water daily but if the nutrients are not excessively hot, that would probably do the trick. You could also use a plastic or vinyl tube for the coil but metal will transfer the heat better.