That's should be the best temp your fan can provide u with already.
Anyway even if u can achieve 27 or so also no use coz it will not stay there permanently. Temp will fluctuate due to the surrounding temp also.
If raining day more cooling and if hot n sunny day u can even c it climbing to 29 or so.
depend what u wanna keep.
If mainly wan low temp only,
dun locate your tank too near to wall, (at least 4" away)
direct your fan 45 degree and blow across the water surface,
dun use wavemaker,
dun use any form of lighting.