Question: I recently did a 25-percent water change in my reef aquarium, and later that same day a film of green algae appeared on the glass. I cleaned it off with an algae magnet only to have it reappear just a few hours later. That was about a week ago. The algae film seems to be getting a little lighter every day, but I’m still having to clean up algae. Have you ever heard of this happening? What could be the cause? -Personal communication from fellow hobbyist

Answer: I’ve not only heard of this happening, but I’ve also experienced it firsthand on more than one occasion in my many years as a hobbyist. The broad explanation for the bloom you’re experiencing is that some aspect of your water-change procedure is either introducing or liberating the dissolved nutrients that are fueling the algae MORE