For those who are using tap water for top-off or water changes:

Tap water sometimes contains copper to kill unwanted things. Algae eats copper, as long as the copper is not added to much, too fast. If the copper is added too much, too fast, it will stop the algae from growing for a while. So to prevent your scrubber from being affected by this, try to make sure you have as much algae on your screen(s) as possible when you add the tap water. In other words, don't clean your screen(s) before you add the tap water.