Hi. I have two large tiger oscars in a 70gal tank. Over the past few months, I have noticed a buildup of some small crustaceans on the tank sides. They range from barely visible to about 3mm across, are immobile, have a chitinous transparent shell, and have visible internal organs. They appear scale-like, but are smooth and round shaped. They appear to collect more toward the top of the tank near the waterline as well. They are not attaching themselves to the fish, so I am not that concerned, but what the heck are these things? They are kind of a pest to clean up. Any clues?