Hot tub scaling

What would you recommend using to get rid of hardness buildup. There's a layer of the white build up on majority of the hot tub surface and I've used HCl, toilet bowl cleaner, CLR...everything I could think of to try to get it off and nothing seems to work. The only thing that some what works is if I scratch it off...but this I trust you have a better option. The majority of the websites I've consulted offer what to do to prevent the build up but nothing in the way of removing it once its here. Please help!!!!

Unfortunately you have tried all the things that we would recommend. CLR is preferred by most of the spa manufacturers to remove the scale. It will take elbow grease and time but, using a stiff scrub brush with the CLR will eventually get the majority of the scale off of the spa. (I sometimes have to get in there with just my finger nails). Once you have it down to and acceptable level then I would use some sort of sealant or gloss to try to prevent it from coming back. I hope this will help.