Fluro ballast ratings

[Grug]

Hi there..

i have a Aqua one 620T with standard lighting hood.. it came with 2 x 18w power compact fluro globes.. there is enough room in there to run 1 x 24w and 1 x original 18w globes and i would like to do this.

Question is.. will it damage the ballast if i put in a higher rated / non matching globes..

Thanks in advance..

Grug.