Best way to restart tank due to Dino's!!!?!!

[Reefer6]

I had dino's in my my first reef a 55g several years ago. I dosed hydrogen peroxide and it worked very well; it got rid of the snot. I didn't do a blackout but that would have helped. A great way to tell if they are dinoflagellates is in the morning they appear to have gone a way a bit from the night time but after a full day of light before the light turns off the dinos appear to have reound and doubled in size. This tank was also new probably under 6 months when I did the peroxide treatment

 

[Fate]

What causes that algae to bloom? Overfeed?