Do you use any of those toilet bowl cleaners or dyes?
I have seen those dissolve and accumulate in the tank.
I suggest that you clean and disinfect the inside of your tank. Close the toilet stop valve and flush the toilet. Then using your toilet bowl brush, physically clean the inside of the tank. Open the stop valve and let the tank refill completely and then flush to rinse out the tank. Wouldn't hurt to rinse a couple of times.
After rinsing he tank let it fill completely. Hold the float mechanism down and let the tank fill until water runs down the overflow tube. That will ensure the maximum level of water in the tank. Add a cup of bleach to the tank and let sit for about an hour.
Stop using any additives, cleaners or dyes that you may have been using.
To insure that the slime is not caused from bacteria in the water supply, clean and fill a used milk carton with water. Rinse the milk carton well and disinfect with a small amount of bleach. Fill milk carton with water from a lavatory faucet. That will insure that the water in the milk carton pass though the same pipes as the water n the toilet.
Sit the carton of water aside (opened) for a couple of weeks to see if any bacteria develops. If any does contact the municipal water supplier.
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