The most common causes are over/under-watering, too high a level of soluble salts in the soil (plasmolysis aka fertilizer burn), too much sun @ midday. The 'over-watering' issue could be from a collapsing or poor soil, even if you think you're not over-watering. When you're growing in a shallow pot, even a soil that supports only a half inch of perched water is unacceptable. If your pot is 3" deep and the bottom 1/2" of the soil is saturated, that is about 17% of the soil saturated - enough to root roots, impair root function, and cause the marginal or tip necrosis you inquire about. Al

Your tree is certainly being tortured by multiple causes. Avocados like high nitrogen food on a regular schedule. You actually have some fruit on your plant that does not have enough energy to grow leaves, remove the fruit. I would take the whole container and immerse it up to the rim in a tub of water, preferable water without a lot of Boron in it. Does your water source not make available a test report on the water they supply? After you remove the container from the soak and it drains the excess water, I would dissolve a table spoon of avocado labeled food such as that available from Lily Miller or if not available, Miracid or other citrus/avocado food per gallon of water. Good luck on your tree rescue. Al

a pic would be helpfull. what type of potting soil did you use ? is it in full sun ? if the plant is in full sun and growing fast,, it needs more nutrients. if you used a potting soil that doesnt really have enough, then its a problem. i would also check moisture. put your finger down an inch or 2 in the soil. it should be damp, but not wet... i add mulch to the top of my containers, just like i do to my plants in-ground. - compost is even better! it keeps the soil damp, but not wet, and you dont have to water as often starfruit like to dry out between waterings. (maybe the container soil is holding too much water, or, you are watering too often ?) the brown tips usually means lack of water OR, over-watering , white could mean lack of nitrogen, but its hard to tell without a pic. if its growing fast, it needs nitrogen. i would use worm tea, or compost tea, or maybe a fish fertilizer. it will take a few days for organic fertilizers to be taken up by the roots

I've been looking into lights at Amazon and similar places, mainly because I don't want to take a long bus ride to the nearest Walmart or similar store. I note that grow lights now come in all shapes and sizes, including shapes and sizes that can be put in regular light fixtures like old-fashion light bulbs. You would want to make sure that any unusual bulb didn't stress or overheat your lamp. Currently I use fixtures (often called under cabinet light fixtures) with 2-foot long bulbs, and I have one elderly (+20 years old) shop light with 4-foot long bulbs. In both cases a mix of cool white and "grow-light" bulbs. You can also find info on YouTube, searching "grow lights". One video talked about those new lights with red/green/blue bulbs, testing them vs fluorescent grow lights. Poster wasn't impressed with the fancy lights... Anyhow, there is a lot of info out there so you can make an informed choice :)