If you don't have something like a cold concrete floor for your res to set on, you will likely need a chiller. If you can keep the water temps at or below 70F, you can probably get by with just adding beneficial microbes. But if your water will routinely get above 70F, your chances of root rot sky rocket and your overall speed of growth will be reduced because warmer water has less of a capability to hold O2.
*EDIT* One thing that helps me get by without a chiller is, at lights off, bringing the ambient room temp down to about 60-62F. The water's temp slowly drops to the low 60's, and by lights on it's usually right at 60-62F. This way, by the time the lights run 12 or 18hrs and kick back off, the water temp has only risen to about 68-70F. Good luck!