Rocoto has Spots on leaves

Both of my " mini Rocoto brown " plants show what you see in the picture : leaf tips dry off , black spots on and under leaves mostly near the tip . All leaves bend/curl downwards , older leaves get it first . Big pot , fertilizing should be ok ( hakaphos soft elite ) including calcium/magnesium . None of my other chilies have that , no pests at all . Any ideas ? Thank you