28°C

28c isn't too hot, but you can increase airflow using an inline exhaust or inlet fan, and that may help bring your temps down. You can also supplement CO2 and the plants will withstand higher temps, but use much more water. I usually be careful about going over 30c if you don't supplement CO2, although some strains actually like it in these ranges. If they start to show negative symptoms from heat and you can't get the temps down, I would just re-raise the light a little bit. I hope this helps, Good Luck!