Your pic is awfully familiar to me just like how mine looked like.
My experience is manual removal is helpful but not a solution. The aim is to help competition not to kill Dinos.
I think you have Amphidinium based on the picture but you have to be sure. Get a microscope to ID it. Cost you about £30 on eBay for a used one. Good ID will save you money and time.
My action plan would be ;
1. Get a microscope and ID the buggers
2. Rase the no3 to 10ppm and keep it there for a while to help competition.
3. Based on ID start UV and/ or silicates dosing
4. Add competition in any form available (rock/mud/bacteria
5. Manual removal siphon trough 5 micron filter sock/ hanging filter floss etc
if Interested my fight you will find it here
I have had aquarium since I can remember. Ok the very first one hardly can be called an aquarium as it was just a 3l jar with a 2-3 inch catfish in it my dad caught while we were fishing. And that fish didn’t last long with me as he had to go back to the river Danube. It was growing faster and...
www.reef2reef.com
also attached help for the ID part
good luck. There is life after Dinos