it has been like this since they started....it is a durban poison and was started in good soil so not sure why this has happened and its only happened to this plant.
whats up with the soil? light conditions? watering schedule? fert history? im not expert, but it looks like a pH problem. or massively overwaterd
ummm I odnt know if it is over watering or a pH problem because the leaves were like that as soon as it broke through the soil as a seed and well none of the other plants look like that and I have been using the same method to water them all. I have fertilised her once with miracle grow it is under a 400hps and the pH is and has always been around 6.5-7.0. i water them when the first inch or two of soil is dry and the pots are light in weight. I have not fertilised agian as the guy i got the soil off said I wouldn't need to until the flowering period.
One of mine went like yours earlier last year and a feeding of epsom salts (magnesium sulphate) cleared it right up. Dosage is about a teaspoon per gallon of water. I would never has worked it out if it weren't for Sidious. What a grower-dude! Sounds like you got everything else about right. It might be time to start thinking about introducing ferts (half-dosage to start with) cuz compost/potting soil, even the best, will only provide adequate nutes for about 4-5 weeks. Chill...
have two plans that are two weeks old with these necrotic spots on the first set of leaves the other six are fine. There in a 10 above my garage probably not as warm as it should be in humidity maybe a little screwed up. Under a hundred 50 watt high pressure sodium not to close probably a foot away. And they're in Happy Frog soil no added nutes just 6.5 pH on RO water