Burning tips is a sign of nutrients excess , dark green leaves is a sign of N excess. Water with plain water during the next watering to low the output level but don'worry , in coco my input in 1.8 and my outputt is around 2.2 without any issue because when the ec is too high I am watering with plain water to low it ( generally i goes down to 1.8 , can be 1.7ec but the next time it get to 2.2 and I 'm repeating the operation