A picture would really help figure this one out.. But with that said, from your description, it is a school book example of nute burn/ Nitrogen toxicity. If too strong nite concentration is used, it showes first on the lowest leafs. Start with tips gettin burnt and spreading upward the leafs and plant.. Is your fan leaf also turning dark green? (afain from the bottom up) This is a definite sign of too much Nitrogen in your pot.
Its important that you flush out all excess nutrients from your pot, or you may experience the horror of toxic salt buildup on your growing media.. When and if this happens, it's a real bitch getting your grow back on track!
A tip for avoiding overfeeding your plant:
Less is more! If the bottle sais to use.. Lets say 4ml pet liter of water, you seldom need to use 2ml, i e 50%, especially at the beginning, and small or slow growing plants. High temperatures and other environmental issues are also reasons to lighten the nute solution.
To flush out excess nutrients and /or salts from yoyr growing media, do like this:
Mix nutrient sollution at 25-30% of what you normally use, except for any magnesium additive you use when growing in coco coir. pH the water solution to desired level (hydro @ 5,5-5,9 and soil @ 5,8-6,5 pH).
Run at least 2x the pot size of water slowly trough for two days in a row.
For even better flushing results, add some yucca extract and enzymes to the flushing solution.
Good luck!
