Burning from nitrogen toxicity......the super green leaves are the give-away clue.
Remember, in soil it is a schedule of plain water/plain water/feed/plain water/plain water/feed..........
Your plant needs a chance to use up what is already there, before new nutrients are added, otherwise nutrient salts build up and cause burning to ......... leaf tips!
Watering to run off each time also helps prevent the build up of nutrient salts in the substrate.
Force feeding your plants is a no-no.
18/6 is also much healthier for them, they NEED adequate sleep.