Most common 250-watt single-ended lamps recommended for that ballast include:
Aquaconnect 14,000K
Aqualine AB 10,000K
BLV Nepturion 10,000K
BLV Nepturion 14,000K
BLV Nepturion 20,000K
Giesemann Megachrome Marine 12,500K
Giesemann Megachrome Coral 14,500K
Giesemann Megachrome Blue 21,000K
Phoenix 14,000K
Radium 20,000K
Ushio Colorlite Blue