When topping off evaporated water from your aquarium, the usual entry point for the water is the sump. Automatic top off systems slowly add water to the system until the proper sensors are triggered to shut the feed pump off. But if you don’t use an automatic top-off system, you probably use a big bucket or some other manual means of adding large volumes of freshwater to your tank. This system has a few inherent issues, the big on being a sudden change in salinity. Another, less obvious issue is the possibility of stirring up all sorts of detritus and dumping it into your aquarium. If you vacuum this debris when doing water changes, then you may not experience any issues. But if you let that stuff sit in the sump and accumulate, then you could end up relocating it all over your corals when you top off. To summarize, there are two morals. One, don’t let detritus accumulate and two, find a method of slowly dosing freshwater to your aquarium instead of doing it all at once.