could be ur light to close to ur plants use +-30cm check ur hand if it gets warm for ur hand its warm for ur plants to !
or nutes? u feeding them to much shit? try only water them with clear ph5.5-6.5 water.
info on soil u use? nutes? pics?
normally if the leave tips are curling down and turning brown at the end tips of the leaves its due to a few different reasons, anyone one of more than one can cause this:
1. first and most importantly, CHECK YOU SOIL/RESERVOIR FOR ANY PESTS/MITES. ***when you do this, make sure to use a magnifying glass for inspection because normally they are extremely hard to see with your naked eye. if you do have mites/bugs, let your soil dry completely bone dry until the plant is showing signs of drooping "this wont kill the plant", then flush with a water/peroxide mixture of 3:1 (3 parts water, 1 part peroxide). saturate your soil with the mixture until its nearly dripping from the bottom. the peroxide mixture will not hurt the plant, its actually beneficial. wait at least two to three days and inspect your soil again for mites/bugs and if they are still alive, treat again after one week. "use plain ph'd water in between treatments. *** you can also sprinkle cinnamon on top side of soil to deter soil mites/pests ***
2. nutrient burn can cause tips to turn brown
3. high temperatures in the room/tent can cause curling. in my experience I don't recommend exceeding 85 degrees and nothing lower than 60 degrees.
4. ALWAYS GIVE YOUR PLANTS A GOOD FLUSH ONCE HALF WAY THROUGH VEG, AND AGAIN HALF WAY THROUGH FLOWER TO REDUCE SALTS AND NUTRIENT BUILDUP.