Please don't spam when you don't get a response straight away. Assuming you mean 80cm long and not high as you haven't specified. I would think that you'll be fine as that's only a 10cm gap at either end. Play around with the settings and see what you like, are you low-tech or high-tech? Start with lower power to begin with.
another thing but is it necessary to add the side reflectors to increase the light or are they not needed
Yes, more than sufficient.Hi, I wanted to know if my 60 cm Chihiros WRGB2 is sufficient for an 80 cm aquarium