Thanks, John. Would anyone else care to share their opinion as to what's happening with this little plant?. I've looked on this site and couldn't find anything that remotely looks like what I'm dealing with. I thank you all so much :-)

Sean, as long as your Vigoro has micronutrients, that's fine, but I would also hit it with a foliar application of Grow More Citrus Growers Blend. It is something you want in your "citrus arsenal" here in S. California. With all the heavy, cold rains we've experienced in the last 2 years, you're going to run into the same issue I have with citrus in the ground (my soil is mainly DG here in N. San Diego county near the coast): a leaching of micronutrients, especially magnesium. So, start with the Vigoro, but do make a foliar app with some micronutrients. You'll see the difference, promise :-) And Tim's right, no pruning for now. Wait until you obviously need to do some MINOR shaping. Remember, with citrus, pruning equals no fruit. Citrus produce fruit at the tips of their branches, so you're cutting off your next fruit crop when your prune! And Tim's advice about removing suckers is right on. Just break them off if they're soft. If they've hardened off, trim close to the rootstock. Our water isn't too alkaline here in San Diego county - about 7 to 7.6. Fine for citrus. But, for your little guy, acidifying the water with some vinegar and pouring it over the fertilizer may help prevent the micronutrients from getting locked out due to the alkalinity. You guy needs a bit of a rescue. Tim's advice is good. Once recovered, you probably won't need to acidify your water. You can also achieve this with your foliar application - acidifying the water you use to dissolve your Growers Blend in. When you pick up your moisture meter, pick up a decent pH meter (don't buy the cheapest one). It's worth having these in your gardening tools. I've had both my moisture meter and my pH meter for many years. Great tools to have! Patty S.

Thank you! I did fertilize it with an slow release organic all-purpose fertilizer (10% nitrogen, 2% phosphate, 8% potash, 1.8% calcium, 3% sulfur) when I first repotted it so, so maybe it's hitting the tree now? I was worried that the cause was fungal, overwatering (although I've been very good about not "overloving" my tree) or even some nutrient deficiency/imbalance. Would it be better to leave it be (let the existing fertilizer leach out) or should I "treat" with a citrus fertilizer? Thanks, again, for your advice!

Have seen things like that before on the underside of my leaves also on occasion. How are you treating your tree for pests?