Join Date: Jul 2010
Location: Outside Philadelphia, PA
Yes and no. For the size tank you have and the amount of lighting, 10000K verses 6500L bulbs don't make too much difference as far as growing plants. You have plenty of light.
However, 6500K bulbs have a very yellow tint to them. Think of incandescent lighting or a sunlit pond in the late afternoon when everything looks golden. 10000K bulbs look much more blue, looking like mid day.
It comes down to what do you like better over your tank, and as you found the 6500K bulbs cost less. Since your fixture has two bulbs, you can also use one of each.