That is not dinoflagellates as there is no stringy bits with air bubbles attached.
That looks like a mix of diatoms and hair algae.
Is this tank fairly new as it's all part of the maturing process.
Using tap water is not ideal you should be using RO Di
water with a 0 TDS
Lower your phosphates and nitrates and it will clear.
What's your current phosphate and nitrate readings.
What filtration do you have on the system