Can you post a picture of the whole plant?
Often on my own grows the lower leaves die off. It really isn't anything to trip about, or to start treating for a problem when there isn't one.
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In this picture you can see what I'm talking about. Sometimes, the damage is done, and the plant is perfectly healthy despite a single sick leaf at the base of the plant.
These leaves are the furthest distance from the light and when the plant is in immediate need of some element it cannot uptake enough of these leaves are cannibalized. To think you need that 3-bladed leaf from start to finish to indicate a healthy plant is to focus your energy in the wrong places.
I think you should follow the directions on the PBP at about 2/3rd to 3/4 strength, your plant is probably due for more food anyway now that it is older, but don't go treating an issue you might not actually have based on the diagnosis of just a handful of the bottommost leaves.
A full photo of your plant would make it much easier to determine if there is a nutritional imbalance whatever the cause. Personally, I think your plant is fine. Mine do this shit sometimes when I let the media get dry for just a touch too long. Maybe that'd explain it. A one time "woops" which could only be compounded into a larger issue if you start to overfeed.