Ring around the collar?

[MonkeyBrain]

Picked up a used Marquis Spirit the other day. It was filled, heated and running when I went to look at it. Everything worked fine, but I noticed a white ring around the entire tub. I was able to scratch off the residue to expose the acrylic surface underneath.  I am not sure if is chemical residue or minerals from the water. The woman who sold it to me was not sure either. She had bought the house and didn't use the tub. It sat for over a year. The electric was on and the tub did run every 4 hours. The cover was shot though. I drained the tub before transport. It rained the other day and the tub had a few inches of water in it.

I was going to go to wall mart and get a hard water remover, but after reading this forum I figured I'd consult an expert. I went to the local marquis dealer and he sold me a cleaner called Robarb Clean-A-Way and a scouring pad.  He told me that I should not use anything stronger than this. I scrubbed for a few hours and got a good deal of the redidue off, but I still have the "Ring around the Collar"  I am able to remove the residue with a screwdriver, but I know this isn't the way to go either, besides it would take a million years to get into all the nooks and crannies (What is a cranny anyway?)  Any suggestions?  

BTW. I looked in the chemicals she had given me with the tub and guess what was included? Good old Robarb Clean away and some metal stuff that I also bought from the dealer. Shucks! No big thing, I needed to make friends with him anyway.

Once last thing I thought you might find funny. While looking at the spa I had opened the cover to make sure everything was on the up and up. I went with the woman into her house to trip the breaker so I could look at the electrical panel in the spa without getting zapped. We were gone for 15 seconds tops! When we came out, her middle daughter (8 Yrs old ) had jumped in the tub with all of her clothes on. It was hysterical! The woman didn't find it funny though? "See why I need to get rid of this thing!"
 Anyway,
any suggestions you have will be greatly appreciated.

[J._McD]

My guess would be calcium deposits.  This would be consistent with well water if that was the type of water in the community.  If it wasn't well water that still does not rule out calcium.  Once attached to the acrylic, it is tough to remove, maybe others will have a recommendation or check with the dealer.  

[HotTubMan]

My guess would be calcium deposits.  This would be consistent with well water if that was the type of water in the community.  If it wasn't well water that still does not rule out calcium.  Once attached to the acrylic, it is tough to remove, maybe others will have a recommendation or check with the dealer.  

When I worked in Burlington Ontario, we had this problem with our first pearlescent acrylic tub. It was very difficult toremove. We did not have hard water either (85ppm out of the tap, we boosted it to 150ppm). If memory serves, the Mr.Clean magic eraser worked.

[hymbaw]

Try putting some ph decreaser in an old sock, get sock wet, rub away.