I am still having to dose Seachem Flourish for phosphate a couple of times a week. Not having to dose nitrate though. Holding steady at around 4. If you can bring my a small sample of the dinos I have a microscope and we can get a positive ID. Some species are very susceptible to UV. I started UV and had mine almost eliminated in about 24 hours. Do yours markedly decrease during lights out and get worse when the lights come on? If so it's likely one of the species that goes in to the water column at night and would be treatable with UV. You could borrow mine if that's the case.