What do you mean by completely cleaned the tank?
To have a healthy tank, you need a biofilm of beneficial bacteria covering all surfaces, and media in the filter.
If you've taken everything out, thoroughly cleaned it off, you may have destroyed that needed biofilm which helps you cycle a tank.
That biofilm consumes ammonia and other waste products given off by the gills, and in the feces of fish.
If that's how you cleaned the tank, doing large water changes are what you need to do to dilute ammonia and other toxins.
It usually takes 4-6 weeks to successfully cycle a tank.
The fungus (or bacterial infections, many look similar) may be due to stress, if your tank was not cycled.