My understanding is that Spot's shell problem was caused by him not basking nearly enough (he almost never completely dried out) and when he did, he didn't have any UVB so I suppose he wasn't metabolizing calcium very well.
I wasn't keeping his water clean enough either. Also, our tap water's ph in Mesquite is quite high - around 8.8.
I was told by some people on here that know what they're doing that to correct the problem I should correct the habitat deficiencies and with time the scutes would shed. Also, someone (Reptilegirl in Houston, I believe) said that her turtle had shell trouble when the water was very alkaline but that his fungus healed and he started shedding again when she lowered the ph.
Here's the thread with that discussion:
http://www.redearslider.com/forum/viewt ... highlight=
As long as Spot was out in his pond in the sun last summer his shell improved pretty quickly. Big pieces of scute were coming off. I think it's still making some progress now that he's inside for the winter but not as fast as in the summer. Little pieces of shell chip off but not whole scutes.
When Spot was outside in the summer sun he basked a lot. His shell dried out and he got really good UVB. He basks inside too but I know it's not as good as natural sun. I recently got a better UVB bulb - a T-Rex 100 watt flood - and I'm hoping that the increased UVB and heat will entice him to bask more and that he'll get more benefit when he does.
I never put peat moss in the water as discussed in the thread. It sounded like a horrendous mess and Spot really needed to be absorbing his calcium. Instead I used a product called PH Down. Apparently a couple of weeks ago i got it too low (around 6.4 I believe) and killed the bacteria in the bio filter! I then raised it a bit (to 6.6 to 6.8 ) by adding tap water and the good bacteria are now thriving again.
If anyone uses PH Down, be very careful with it. Some people on here really object to it but with our water being so very alkaline and Spot having shell problems I felt I needed to do something. It's just sulfuric acid and would seriously burn your turtle if you got it on him directly. You have to dilute it BEFORE you put it in, and add it only very very slowly. The benefit of having slightly acidic water is that it inhibits the growth of bad bacteria and fungus. And it may help scutes to shed.
I'm sure Spot wouldn't still be having trouble with shedding if his shell hadn't gotten so bad in the first place. Normally, with a setup like I've got now in the house, he should have a healthy shell that sheds a whole scute at a time, like other people's turtles.