Citrus yellow/narrow/curly leaves, immature fruit drop
I live in the Bay Area. I have posted a picture of the sadness that is my potted dwarf clementine. I got this tree from Home Depot 4 years ago. That was the last time it was healthy. It is still only 3 feet tall and 2 feet wide. I feel like it hasn't grown at all since I bought it. After I bought it, ants got to it and there were scale insects everywhere. I used rubbing alcohol to get them off and the ants have been gone for a while but I think are coming back. But since then this tree has been very sickly and never has produced again.
I have attached a picture of one of the curling leaves.
You can also see that the rest of the leaves around that curling leaf are yellowish and very small/narrow. You can see how small they are in comparison to my fingernail. I have small hands.
There is a tiny little clementine fruit in the photo that will fall off in a few days. All the other ones have fallen off while that size.
There are spikes growing off the branches, and some of them have tiny black specks that look like scale insects, except I can't rub them off.
Other leaves have brownish gunk on the undersides of them that looks like gunky sap.
Please give some advice about how to save this tree. It has a host of problems and I don't know where to start. I currently water it with a drip system of 10 minutes 2x a day, once in the morning, again in the afternoon. Every three months I feed it with Vigoro brand citrus/avocado tree fertilizer granules, about 2/3 tsp at a time. It gets about 10 hours of sunlight. it's in a hardy plastic, 20 gallon planter. What should I do? Thanks for your help!!