Hey, buddy! 👋
This is magnesium deficiency, but it's hard to say exactly why, you don't have this diary, no records about nutrients!
1. Either you have tap water and you're not letting it sit for two days before watering to let the excess chlorine evaporate (chlorine excess).
2. Or you have too much nitrogen in your watering.
3. Or you have too much calcium in your watering (cal/mag + nutrients + hard water).