My favorite cleaning tool for calcium buildup is a toothbrush. Just a plain, clean toothbrush- generic brand. You can probably get one for 50 cents at the grocery store.
I use a product made by Aquarium Pharmaceuticals called, "Safe & Easy."
Instead of spraying it on places like the hood and filter parts, I like to just put a few drops on each area to be cleaned. Let it sit for a couple minutes, then use a toothbrush to rub it really well, then wipe away with a clean paper towel or rag.
To clean the front of the glass, obivously it does work well to spray and wipe with a clean rag.
A toothbrush is also a handy tool for cleaning the hard to reach spots such as along the seals in the corners of the inside of your tank. Lots of great uses for a toothbrush in your aquarium. A clean, new, toothbrush.