Many people invest their time and money trying to create the "perfect" environment for the fish they have, temperature, lighting needs, feeding, decorations, etc. But at the same time, we strive for that perfect, clean looking aquarium. But this is not even natural. We then invest more time and money on how to get rid of algae when we are in fact creating the perfect breeding ground for them in the first place! If you ever take a look at videos of tropical fish habitats in the wild, they come from murky lakes and rivers with algae growing on practically everything! Fish also feed off of the microscopic organisms living in the algae. I know, I know, the point is to enjoy the look of an aquarium but some algae is good I think if you have a couple of algae eaters in there. All I'm saying is, the "Why is this happening?" sometimes is not your fault or always controllable.