Hello all. Is this a parasite? if so, which one? (Aquarium details at end of the mail) Story: Some 2 weeks ago we introduced few new fish, and then the problem started.(were quarantined before that for 2 weeks) we always pick up those Corys from shops that look not the healthiest and have least chance of being sold or are left alone in the aquarium. Our Corydoras Black (schultzei) and Panda's cory's seems to have a grey-ish layer over them, (like old chocolate has) If we check with a simple magnifying glass you can see that it are small separate grey/white dots, like very very small fine sand, which move quite smooth over the fish skin and eyes (only see that while looking through magnifying glass, and even then you need to look very good, with bare eyes you don't see them at all like this) Both type's of cory's are flashing through the sand sometimes (couple times a day) No scratching against objects, few are often on the surface for a few seconds drinking air) Fins are deteriorating slowly) Most of them are quite lethargic, We lost few of them recently, one in this aquarium, and he did have these bugs/parasites. After that we treated them with JBL - Gyrodol plus 250 (100ml contain: Praziquantel 1500mg) Against skin worms and gill flukes. (date by far not expired) 1 treatment, but the bugs/parasites are still there, tho the fish react a bit better, more active and eating better. So, anyone knows what this is? can't get smart on any blog/forum/or website. Aquarium info: Total swimming friends in aquarium 3 C. Schultzei (we are looking for more) 8 C. Panda's Cycled aquarium. Total running time approx. 2 months. Aquarium: Aquarium Juwel Rio 240 (approx. 190 liter water) Daily 25% water exchange (prepared with Sera aquatan) Temp. 26° C. 2 pcs of Mopani tree root Planted aquarium , mostly slow growth, with few Hornworts Sand substrate average 2.5 cm thick Filters; 4 sponge filters for 200 Liter each + 1 aqua-el Turbo 500 filter (for flute connection) (350L/h) Water value's (by Sera liquid tests) Nh3/Nh4 - 0 mg/L No2 - 0 mg/L No3 - 2 mg/L Ph - 8 Kh - 7 dKH Gh - 9 dGH Results are steady for 2 weeks like this. Thank you for any answer or clue.