Shell rot usually results in softness and darkened spots on the shell. This sounds like fungus. There are two things you'll need to do to treat this at home. The first oen is what you've been working on - making all conditions optimal. However, if you got your information on care from a pets store, you have probably been misinformed. That's very common. fungus often occurs when lighting and temperatures are not quite right. I'm going to send along my slider care sheet, which will give you the exact information you need to keep a turtle healthy.
Now for the fungus. The most effective method involves what is called 'dry-docking.' You'll need to prepare a 'hospital' for the affected turtle. A large plastic tote works well. It should be equipped with a basking area at 90*F and a UVB light. The turtle will be kept warm and dry, except for a 30 minute bath twice a day. The two baths are very important to prevent dehydration. Feed during the bath. After each soak, scrub the shell with a clean toothbrush with Betadine (available in drug stores) on it, but try not to get it on the skin, and especially avoid the eyes. Do this twice a day. Follow that with a coating of anti-fungal cream (the kind sold for women to use to treat yeast infections). It can be put on both the skin and shell, if there is fungus on both. If the problem doesn't clear up within two weeks, you'll need to have your turtle examined by a reptile vet.
PimaFix is made for fish, and fish products may not be effective on reptiles, and many of them are dangerous. I wouldn't use it again. You can use one of the sulfa bath products sold in pet stores for turtles. They are added to the tank. This method is much less likely to be successful than si dry-docking. With this method, too, a vet should be consulted if the fungus isn't gone within two weeks. If your turtle also has some early shell rot, the dry-dock method will help, but the sulfa bath will not. This link will take you to a directory of vets if you end up needing one:http://www.anapsid.org/vets/index.html#vetlist
If you have more questions, let em know by clicking on REPLY. I hope the fungus will quickly clear up. The care sheet follows.
(If you find my answer helpful, please click on the green ACCEPT button. Thank you.)SLIDER TURTLE CARE SHEET
Well-cared for sliders can live 30 years or more.The Tank
It's recommended that a baby slider have at least a 15 gallon tank. By the time the turtle is 3-4 years old, it will need a 60 gallon tank, so it's best to get the biggest you can in the beginning. You can also use a large RubberMaid tote. That's not as pretty as a tank, but costs a lot less. Set up the tank so there's a land area and a water area. Put the basking light at one end so the whole tank doesn’t get too hot. You want the water to be about twice as deep as the turtle is long. If the turtle is two inches long, you'll want four inches of water.Temperatures and Basking Area
Turtles need certain types of lighting and need to be warm. Air and water that are not warm enough can lead to fungal and respiratory infections and unhealthy shells. Turtles must have a basking area where they can get out of the water, dry off, and bask in very warm light. The ambient air temperature in the tank should be around 75 *F (24*C) , with the basking area warmer still. Over the basking area there should be some sort of lamp that will take a 40-60 watt incandescent bulb (or you can buy a ceramic light fixture made just for reptiles). If you live in an area that has farm stores, you can buy a metal light fixture made to keep baby chicks warm for just a few dollars. Don't buy the accompanying bulb, however. You need an ordinary incandescent bulb in the basking light. Hardware stores sell similar fixtures as work lights. The basking area should be kept at 85-90*F (29 to 32*C). Use a digital probe thermometer to be sure. You can adjust the temperature by raising or lowering the light fixture.The lights that come with the covers on aquariums are not suitable for turtles. You'll also need a submersible aquarium heater that will keep the water 78-82*F (26 to 28*C).UVB Light
It's extremely important that you buy an additional light that produces UVB rays. A Reptisun 10.0 is a good brand that does. If you choose another brand be absolutely certain it provides UVB rays. Don't take the word of pet store personnel, but read it for yourself. Full-spectrum, DayGlo, sunGlo, UV, or UVA are not the same thing. I'm putting a lot of emphasis on this because it's crucial to your turtle's health. Without this light, Metabolic Bone Disease (MBD) will develop because your turtle won't be able to produce vitamin D. Vitamin supplements are not a good replacement for the proper lighting. MBD causes a very slow and painful death.UVB bulbs must be replaced every six months as they lose their effectiveness after that, even though they may still look fine. Light that comes through a window isn't sufficient because the glass filters out most of the rays turtles need to stay healthy. To prevent MBD, turtles also need calcium. The easiest way to provide it is to place a cuttlebone in the tank. Cuttlebones are sold in bird departments of pet stores.Filtration
Turtles are very sensitive to water quality. Even if you change the water every day, it can still contain harmful chemicals. A good filtration system is essential. Water changes are also needed even with a filter. If the tank is too small, no filter can keep up with the amount of waste that turtles produce. Feeding
Feeding is an area where pet stores often give out bad information. Commercial food should make up only 1/4 of the diet. Animal products (cooked meat, earthworms, canned cat food) should make up another 1/4. The remaining half should be plant foods (dark lettuce like romaine, bits of strawberry or melon, etc.). Hatchlings should be fed every day. Older turtles should be fed 3 times per week. Overfeeding can lead to gout and kidney failure. For Further Reading
This is among the most reputable sites on turtles.http://www.austinsturtlepage.com/Care/caresheet-red_ear_slider.htmhttp://www.austinsturtlepage.com/Care/cs-yellowbelly.htm