A daylight-balanced T8 tube — the neutral, general-purpose option in the range. Colours read the way they would in daylight rather than being pushed one way or the other, which is what you want if the tank is in a living room and you would rather it looked natural than theatrical. If you are chasing dramatic reds on a show tank, a pink tube does that better.
Sizes
- 33cm — 10w
- 45cm — 15w
- 60cm — 18w
- 75cm — 25w
- 90cm — 30w
- 120cm — 36w
- 150cm — 58w
Match the wattage, not only the length. The tube has to suit the ballast or transformer already in the fitting, and length alone will not tell you that — read the wattage printed on the tube you are taking out.
Replace them about once a year. Fluorescent output and colour shift long before a tube actually fails. One that still lights can be doing well under half the work it did when new, and plants notice before you do.
Run the light on a timer. Six to eight hours a day is a sensible starting point, and consistency matters more than duration.