In theory I would say yes you could have a 'breakout' of DOC
in the water. How? Well the DOC
's will come from the life in the water and the items we put into the water. Stuff like food, top off water, airborn particles all contrubte to the waters quality. Items in the water like bactera, fish waste, decomposing creatures, etc all contribute to the DOC
If you saw the outbreak a few weeks after all the fish was taken out of the tank then my guess would be that the DOC
's where really a collection of bactera that had died of due to the lower ammonia production. Think of the bactera population as a population in contant flux. As more ammonia load is generated more bactera reproduce to cope with the additional food source. As the load is lowerd less bactera are produced and the ones that are in excess die off.
This is only a theory so it could be full of DOC