I called manufacturers on every bulb Walmart sells for my fuge. The only one there (at my local store) that is above 6k is the brinks home security bulb, and it is around $12 bucks. Lowes has them for $7, and I liked their clamp more. The tray their bulbs sits in also says their K rating, so it is really easy to pickout a daylight 6500k bulb. My chaeto has grown about 4x from what I picked up.