without a chiller your not going to get 20 degree sustainable drops. you would literally be changing out your bottles every half hour MAX! if you can get your temps down to 80ish by adding a fan to exhaust your room pick up some stuff called dutch master ZONE! this stuff prevents root problems at damn near 80 degrees it also help with nutrient uptake due to the higher temps. If you can get your room cooled down to 80ish a 2 liter bottle of ice would need to be changed roughly 1 to 2 times during your lights on period. your temps should lower considerably without you lghts on. hope this helps a little bit. the zone is roughly 25 bucks for a liter and a liter last me a whole cycle on 3 systems. all 3 of my systems have 30 gallon rezs that get changed weekly. its like a 5ml to 5 gallon ratio.