1 Inch Tubes?

[Rorie]

I have just acquired some arcadia units for lighting my aquariums.

They say for 25-30w, 26mm tubes.

I gather this means i should pick a tube up to 30w in size, but what is the 26mm about? I dont think thats T5 or T8....is it?! What do i get?

Thanks

 

[StandbySetting]

26mm is T8.