Purpose Quick routine loading $ff into the first five bytes of the Video Memory ($fc00).
Code
	ld a,$ff	;byte to be copied
	ld ix,$fc00	;start address to copy
	ld (ix+0),a	;ix+0=$fc00
	ld (ix+1),a	;ix+1=$fc01
	ld (ix+2),a	;ix+2=$fc02
	ld (ix+3),a
	ld (ix+4),a
	
Error First off, using the Index Registers is not a speed efficient choice. The basic instruction ld (ix+$??),a is three bytes long. It is much wiser to stay away from these registers all together. They are generally one byte longer than using the hl register because they have a byte preceding that signals the processor to use the ix register instead of the hl register. It would also be quicker here to set up a loop.
Fixed Code
	ld a,$ff	;byte to be copied
	ld b,5		;how many times to copy
	ld hl,$fc00	;where to start
loop_start:
	ld (hl),a	;load a at (hl)
	inc hl		;inc to point to next spot
	djnz loop_start	;do it 4 more times until
			; b=$00