Hi Mitch,
Glad to see you post back & let us know. I bet you & family are happy with it. Yes, it is weird to read back from the beginning. Quite a journey you had, & I'm sure you feel much more knowledgeable about the chemistry now. I'm gonna try & answer what I can, but am unfamiliar with a fiberglass surface pool.
1) Is there a cartridge you can just take out & let water circulate through the empty canister? I thought I read that, but again not familiar with the Nature2.
2) Scaling develops from a combination of high calcium hardness along with letting PH get too high. If you're familiar with the pool calculator now, you can do a complete test, fill in your numbers in the "NOW" column & see where the CSI index is. You can do some playing around with the numbers in the "Target" Column" with your TA, CH, &/or PH to try to aim for a lower CSI value (usually maintaining a lower PH is the easiest answer). This will keep future scaling at bay. I usually target a slightly negative CSI in my pool. I won't comment on what to do to get it off your fiberglass, as I'm not knowledgeable enough to know what can be done without damage to the surface. Some of it might loosen in time maintaining a bit negative CSI. Others with more experience will hopefully chime in. If not, start a new thread on the subject.
3) If it's from body oils, suntan lotion, etc, I think a bit higher level of chlorine will oxidize it out, I've heard a magic eraser gets it clean also. I don't have that problem, no women around the house. Just an occasional few of my sons female friends that might use it once in a while.
4) I think the acid in sock method might be most useful for you if its in a localized area, without causing the pool to revolt with a high chlorine demand again. I'm getting a slight staining again on my vinyl liner walls. I use Iron Myte from Menards. It works pretty well taking it back off, but again, it is citric acid based, & have to watch my FC when I use it. I'll probably try again next spring on the AA, but WILL have more patience without adding more, & keep my winter cover on till I can hold chlorine again. I'm also doing topoffs this summer through my water softner to get rid of any additional metals entering the pool.
Sorry for the long answers, enjoy the pool & it feels good to us all to see another success story come across.
Take care,
Dave B.