Do I have to pay fidya (ransom) for masturbating during the night in Ramadan?

I have been masturbating at night during Ramadan. I ensure I do *Ghusul* afterwards, but do I also have to pay some *Fidya* or ransom? Also, does the sin increase if it's done *during* Ramadan?should i do Ghusul before sehri or can i do it in the morning