I have been battling Dinoflagellates for some months now and have tried lots of methods to eradicate them in conjunction with lights out, with each only providing a Dino. free reef for several seconds after lights back on.
Recently, I invested in a 24 watt UV sterilizer for my 30 gallon reef and installed it on my tank. I turned off my lights and covered the aquarium for 3 days. During the 3 days of darkness, I continued to dose H2O2. 1ml of 35% H2O2 per day.
The results are spectacular! Once lights were resumed, no Dino bloom and any remaining Dinos. have slowly disappeared. The skimmer went nuts for the 3 days the lights were off and after the 3rd day, the skimmer collection jug overflown. I have been Dino. free now for 3 almost 4 days now and have done my first water change in almost a month and still no Dinos. bloom as a WC always promoted. For me, even a week free from Dinoflagellates is worth anything as it is the most problem free the tank has been for months.
I am a very happy chap.