well, rule out the overwatering first, since that is least intrusive.
Let top layer dry a bit -- 1/2" to 1" -- before you water again. Check weight of pot when dry and watered.. one more thing to be familiar with that will help you in long-run
N tox will start low and work up - it is a mobile nutrient. (immobile will mostly start where the light is hitting it as it cannibalizes itself and can't get more -- one more way to eliminate possibilities)
Get a leaf chart. i got one in my dairy. right click it and "save image as" .. it's resized on sit, so it's much easier to read when you open it up on a desktop with picture viewer. can zoom in easily etc.
since you recently fed, maybe a little less next time.. see what happens.. trial and error is all we can do sometimes. prefer to be conservative, because its difficult fixing a toxicity compared to a deficiency.
in addition -- know pH of what you add... it can cause any and all nutrient deficiency and toxicity symptoms. so, always get that in balance first before dumping things in.