We had a 10 gallon hex with the 70w viper over it and it filled the little tank nicely with light. When we upgraded from 10g hex to 20g hex, we started out using the same clip on viper, but weren't happy with the amount of light and ended up upgrading the light to 150w clip on MH. The footprint of our tank is quite different though, than your 24. Our hex is probably taller at about 20" tall, which makes a big difference in the amount of light.