I feel for ya. I recently bought a used 29 gallon reef tank. The inside felt like coarse sand paper, some kind of weird calcium build up I guess. Lucky for me it was glass and I was able to use a green pad. I used all the grease up in both my elbows to get that tank clean.
Here's a tip for you to help reduce your work load: Get a gallon of distilled white vinegar, a roll of cheap paper towels, and a spray bottle. Mix 50/50 of water and vinegar in a spay bottle (you can use the vinegar straight but it's not necessary). Spray sides of tank, and sheets of paper towel and stick them to the tank walls. The wet paper towels will hold the vinegar solution and keep it in contact with the tank. Keep the papers towels on for about an hour and spray occasionally to keep them wet. Using this method will save you water and vinegar by not having to fill the entire tank. Discard towels, grease up those elbows, grab your recommended scrubbing device and go to town on your tank.
** Note to new comers: Vinegar is a mild acid and reef safe as long as it is rinsed off. Great for soaking power heads and other aquarium equipment to get that hard to get off grunge removed with ease. Fill a tub or bucket with hot water and a cup or so of white vinegar turn you power heads on and walk away for 30 min to an hour. A little tooth brush action, a quick rinse and your back in business with more than enough time to update that facebook page you've been putting off.