From most accounts I have read, rated filter turnovers are in reality 1/2 that of quoted by manufacturers. This is probably because they quote the filter motor's turnover derived from it's rpm and the impeller size, or the output with no media etc makes - for impresive stats and helps them shift filters.
If 400 lph = 200 lph reality then (200lph / 54l ) gives you 3.7X turnover per hour which is OK and perfectly acceptable I think.