solar t5

That fixture has 4 bulbs on each ballast, so the fewest you can run is 4. They have the 4x54 at a great price again. Most of us are finding 2 and 4 bulbs are more than enough lights.

so I can't just remove let's say 2 bulbs and use only 6?

No, you can't.

This fixture, according to their website, has 2 ballasts and 2 switches. You must fully populate all the lights on the ballast you are using. This means you either run 4 or 8 bulbs. This fixture would be appropriate on a 120 gallon (4x2x2) marine tank with 4 10,000K and 4 actinic bulbs.

Their 4x54 is on sale for 190. With this fixture you can run 2 or 4 bulbs. You can request the bulbs you want when ordering, so you can get 4 10,000k which would be really white, 4 6500K which would be yellowish or 2 10,000K and 2 6500K and run 1 in each bank.