At the same time I've seen "Dino's" appear from a vibrant overdose. And Dino's that disappear with no intervention.
There has to be a connected causality. Like sponges diatoms and silicate. And the odd algae that appear to cycle through an aquarium and disappear. I've had a dozen of those. It seems to use up what it needs and fades.
Craig bingman had a good article on it. Included fluorides and other odd things that get used up.
It so seems like there's an environmental cause at your house or in the tank.
Again. Mind boggling.