Awesome I have mine on for 8 hours, but it varies depending on how many plants you have, and how many nutrients are in the tank. This is ok, but a lot of people who are serious on their plants will use CO2. I don't, YET. Algae can use up nutrients faster than the plants, especially if the nutrients are fluctuating. I have Bristlenose to eat the algae, but they eat the plant leaves too, leaving big holes in the leaves. If the algae gets established on the leaves, it can make it harder for the plants to get the nutrients, hence making the plants ill. Is it brown algae? If so, it's likely to be the "new tank algae" and a scrub with your thumb and index finger will generally remove it for good (or at least that worked for me) I find that if it's in good working condition, it should be flowing like a garden hose does when you water the garden - aka quite quick. Most aquatic plants are actually lakeside/riverside plants that have adjusted to living underwater. Your's will get there, they just need time
Anytime, hope this helps