I've been having an issue with black things (algae?) constantly floating in my toilet. the toilet is not old. The tank is clean, no disintegrating rubber or algae can be seen. I've tried bleach, baking soda & vinegar, plus other cleaners and nothing gets rid of the problem. I regularly put on gloves and stick my hand inside the pipe on the bottom of the toilet bowl where the water comes from to clean that are out. I regularly clean the discharge holes around the rim one by one . I'm not sure where these floaties are coming from. I live in an apartment building and was told by one plumber that once the building stacks are flushed out, the problem should disappear. This was done several months ago and the problem did not go away. I'm at my wits end trying to figure out where this build up is coming from. I'm at the point of wanting to change the toilet but I don't know if that will solve the issue. Maybe it's coming from the building pipes? Any help is appreciated.