Hard to say....but I would think too little water rather than too much. Could also be intense heat.

Harry

Looks a bit like minor fert burn.

Jeff

I've only given it a bit of fish emulsion,b oth 0-10-10 and 5-1-1 mixed together.

I've also got a cup of gypsum in the soil when I initially mixed it

I tend to agree with Harry...most likely lack of water along with your intense desert heat. New growths are more sensitive to the intense heat...try giving the pot some shade during the hottest part of the day if you can. I doubt its the fish emulsion or the gypsum(I use it on all my gritty mix) and never had issues with what you show from it.

The 100+ degrees you guys are experiencing now is "likely" the culprit on those tender new growths. Good luck!

Interesting. I do remember Dr Campbell telling me that the easiest way to kill a mango tree was to plant it with a dead fish. According to him, mango trees are so sensitive to ammonia that the decaying fish would toast it. To my understanding, mango trees tend to like intense heat. Don't they have commercial groves of keitt mangos out in Coachella Valley, CA where the summertime highs are in the low 100's and rainfall is near 0?

Jeff