Hi I would not empty the tank as you have not found the cause,but I would call it lights off for 2-3 days this will not hurt the corals. before doing the lights off clean as much as you can out of the tank vacuum the sand and rock as good as you can do a partial water change. are you using ro/di water , tap water or filtered water. if using tap get some prime it will help with the bad stuff in the water. +1 Christyf5 has listed everything you need to do from here on out. skim a bit wetter do a 25% water change and lights out for 2-3 days then have a shortened light period for a few months till your tank adjusts and ages a bit more. I have found once a tank is established and not much more will be added to it the whole thing stabilizes it's self. As long as you have enough LR and LS or LR and fuge, test your parameters more for the next while.

Everyones system is different.
In my 110g I have never had any problems with this just a HA bloom from a digital timer being messed up found out the connection on the inside of their time was wired wrong. Now I can't grown the stuff in my tank this I can not figure out PH04 is 0.1

But since I upgraded my kids tank to the Bow front I have had some dinoflagellates on the gravel no where else there is lots of flow as the dinoflagellates is not in a carpet but long strings if I cut the flow it becomes a carpet in a day or so. Its not the red algae I have no HA in that tank either so I don't know I just lights out every now and again it goes away and comes back alittle less each time so sooner or latter it will get sorted out.

I would go with what you have and monitor and keep a file on what you are doing to improve the tank and algae problems this will help also document what the out come was after the change. This gives you a reference as to what is working and not you will find the right combination faster this way.

I keep a log on my tank so I know what is happening and what is changing this includs what fish I have and corals when added and if died that is recorded and of what it died of.

Bill