hi All, I hope our resident experts here can help me identify the problems with my grapefruit tree ... it's driving me crazy!

Basic info:

- tree is probably 15 to 20 years old; trying to revive it after it got severely damaged when the property was foreclosed on. It came back beautifully with lots of new growth but it's still not producing much;

- climate: southern CA desert, lots of sun, dry, 100+ F

- soil: the drainage seems fine; I'm still trying to figure out the best way to water it (sprinklers, drips, how many times a week, etc). I've tried to check the nutrients but I can't tell for sure whether it's lacking anything or not; using commercial fertilizer but can't tell whether it's doing good or not

These are the symptoms:

- distortion in new leaves, with tipburn; I don't see any obvious insects, but I've read online that aphids could be the cause of stunted growth:

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- more stunted growth:

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- strange side burning:

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- yellowing in older leaves: this could be natural, but still; I put a healthy mature leaf for comparison; overall, the new growth is much lighter green than older leaves. I've read that this could be low nitrogen.

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- I don't see leaf miners in new growth, unlike other citrus in the property

Any ideas? I'm going to use Neem oil to try to fight potential aphids, but I'm at a loss as the other questions (watering, fertilizing, etc).

Please help! Thank you so much!