Those temps are good, the ideal temp for bubblers is around 21c or 70f, this offers the highest disolved oxygen levels while also being a very comfortable temp for your baby's roots.
It is better to be safe then sorry in DWC because high root zone temps of 80f and over are very bad for bubblers. This is the zone that bactaria and fungus like to grow in, and they will rot your roots very quickly.