Welcome to the boards! What kind of tank Glass or arcylic? Don't use a steel wool or type abrasive it will scratch the tank. I use a Kent scraper with a stainless steel blade. A SS razor would work I think. Just be careful of the silicone in the seems. I don't know if white vinegar would cut that stuff or not. Maybe worth a try, just dilute 3-1/4-1 with water. Definatly you should scrape not scrub.
Good Luck
Tim