How close do you keep your cooltube to the tops?

Im using a 600w hps in a 90x90x180 tent with 4plants in it. I was shooting for more plants but only 4 seeds germed. =/




I also had alot of heat issues since the tent is in a non ventilated walk in closet, but i bought a ice loaded mini ac that brought the temps down to below 30c about 2weeks after i put them in flowering.
Right now i have about 30-40cm to the top buds that i tied down to get more light further down.

But i need to change it couple times per day since the ac runs out of ice and im not always home to refill it.

As close as you can get them the better.

How about that max temp?

Ive heard 30c is top and anything above that will stunt growth, the firs 2weeks of flowering they had to endure up to 35c but they seemed fine.