UFO onc, several leaves have this on the tips

Healthy roots and 2 new growths, and I have to repot it cause it's in a plastic pot an very top heavy. I'm going to give it a dose of epsom salts tomorrow. There's another onc next to it but it doesn't have any spots like this, which for me rules out sun burn. Both get 20-20-20 fert weakly weekly, rain hits that spot when it falls, and they get rainwater when there's no rain. Is this a mineral build up?

Healthy roots and 2 new growths, and I have to repot it cause it's in a plastic pot an very top heavy. I'm going to give it a dose of epsom salts tomorrow. There's another onc next to it but it doesn't have any spots like this, which for me rules out sun burn. Both get 20-20-20 fert weakly weekly, rain hits that spot when it falls, and they get rainwater when there's no rain. Is this a mineral build up?

