If you look up 24/7 weed, tomatoes or peppers you will see all sorts of people on forums claiming 24hr is best and no it's not. Now those plants are more complex than our algae, but it's frequently a matter of debate on plant forums. However enough people claim it gives them greater growth so it seems at least it's not harmful. But they also frequently recommend checking temps and making sure intensity is appropriate and some claim the desired growth type - 24/7 produces bushier shorter plants. No idea about any of that as I don't grow any of the above, but it's interesting to read.