Hard to tell exactly what it is from the picture, but if you’re already fighting dinos, this could just be more of them. Especially after a water change when you’ve added more nutrients to the water for them to feast on.
I beat them in my tank through 2 things:
1) 4 day complete blackout.....get as much of the dinos out with a net (skim off water, scrape off rocks) as you can and then completely cover all sides of the tank with a material thick enough to prevent any light getting in (i.e. cardboard, not a sheet or newspaper). Dinos need light to thrive, so depriving them of light will knock them out
2) To keep them at bay, i actually increased my phosphate and nitrates. I read in multiple places (included R2R) that having measurable PO4 and NO3 in the water will help keep them away. Seemed counterintuitive to me, but I can vouch that it works. Someone smarter than me can explain the actual chemistry behind this

. A few times that I’ve neglected to add supplements or NO3/PO4 (I used Seachem), the dinos would appear after a few weeks. Once I started dosing again, they disappeared pretty quickly. The dosing was just manual - no need for a pump. With my water volume (~600 gallons), I’d add ~30mL / week of each NO3 and PO4.
I’ve also read that many people have had success with using UV sterilizers to eradicate dinos. I haven’t used it since I don’t want to kill anything else beneficial in the water column. But that’s a personal preference - much like most of this hobby, personal preference wins
Hope this helps!