Used properly it will help eliminate algae since it gives the plants the ability to out grow and out compete the algae.
If you are running pressurized then yes turn it off an hour before lights out and turn it on an hour before the lights go on. Why waste gas and your money. You are going here all about other reasons, most of them are not true, if the CO2 is dialed in right no harm will come form running it 24/7.