It’s difficult to determine by the picture in your case, I don’t see the gas bubbles that dinoflagellates normally have, it could be diatoms as you suspect, only way to be absolutely sure is by looking under a microscope.
Yeah kinda hard to see it now, in your opinion should I continue carbon dosing anyway to reduce my phosphate?
No, the only way to carry on carbon dosing safety is to raise nitrates with calcium or sodium nitrate first. Wile carbon dosing you should at all times keep nitrates and phosphates detectable for a new tank I wouldn’t go lower than 5ppm and 0.05 respectively. There is many options available for you if you wish to carry on getting benefits from carbon dosing, for example bacto balance from tropic marine, this product is ideal to use in low nutrient (not zero) as it has 3 macro nutrients in it, by containing dissolved organic carbon, nitrogen and phosphorus.
