Cleaning tank safely from calcium and lime

Question
I have an approximately 6 inch, 6-7 year old female African Side-Neck turtle named Lucy.  She is so sweet and social.  Over the 2-1/2 years I've had her, the calcium and (lime ? in the water) has crusted the upper sides of her tank that aren't covered in water but get the splashes.  They crust up with calcium I'm assuming.  How can I safely clean this off her tank and keep it looking like the clean tank it is otherwise?

Stats as best I can:
40 gallon tank kept 2/3 full of water; heater 75-85*;  40-50 gallon filter with removable filters (one to rinse and one to throw away); aquarium rock floor;  live plants;  sundeck; UVA/UVB heat lamp on in AM/off in PM; 1-plecostomus 4-5"; feed standard turtle food w/calcium, crickets dusted in calcium, an occasional cranberry and a calcium bone.

Answer
Hi Ruth,

Calcium build-up can be a problem if you live in a hard water area.  You can use white vinegar to clean the scale off next time you do a complete tank cleaning.  Try a 50/50 solution first--spray or wipe it on, leave for about 15 minutes, then wipe it off.  Increase the dilution if you need to.  If it's a glass tank, you can scrape stubborn spots with a razor blade. Use a scrubber pad on the sides of the tank every couple of weeks to keep them clean.  If it took two years for it to build up, it may not be a big concern, but there are softening pillows you can buy at an aquarium store to add to the filter, or you can dilute the water with distilled water to reduce the concentration of calcium.  Good luck--hard water is a pain!