Yeah, those crispy tips are burnt.
Be wary of giving N during flower. You are supposed to withhold it to get more budding. The way I give N is when I repot into the pot they will flower in, I mix some fish glop into the soil for the roots to find gradually.
The yellowing lower leaves are normal that late in flower. No worries. But you are going to want to flush out that pre-ferted dirt with copious water.