which bulb should i use

[Macio]

Hi i'm runnning t5 coralife fixture with one 10k and one actinic blue and i've found one of my old t8 fixtures so i want to add it. I've checked stores and they are selling some t8 light bulbs in 10k, 20k, 50/50, and 6k. T8 fixture have only one bulb so which bulb should i put ?