yea, its my fault for having a sand substrate with fish that are constantly kicking up the sand... my 4 pacu and blackbelt all kick up the sand. never looked like that when I had gravel. water quality tests out fine when I test it ever 3-4 days. I've got a water polishing filter pad down in my sump too to help trap the suspended sand particles.
Do you plan on moving the columbian sharks to salt water later on? They will need to eventually. Great cat though! These and TSN are by far my favorites!