What type of medium; soil or hydro? Soil What brand and type of soil? Ocean Forest Indoors or outdoors? Indoors What strain? C99 How old are the plants? 3 weeks from seed What type of lights and how many watts? CFL (4 x 26W 6500K) How far from the lights? 4 inches from tops What is your watering frequency and source of water? About every 3 days with filtered tap water What, how much and when was it fed? NPK? 1/4 strength General Organics nutes What is the medium/runoff pH and PPM if in hydro? 6 What are the temps and humidity in the room? 82F/57% What size pots? 1-gallon smart pots Any bugs? Look real close. Not that I can see I have 2 plants and one of them has a lower leaf with a dried up yellow-green tip. It doesn't look like it's dying off naturally, almost like a disease creeping up. Other parts of the plant look pretty much healthy. Should I cut it off?
Bump If you don't get a reply before to long, I'll tell ya what I would do, but I haven't seen this before and don't want to give bad advice.
Up your ph to 6.5. I'd also prune that bad spot. Incase it tries to spread. I'm not sure what it is, but ph is off which can cause lock outs.