Instructions
Remove the decorations from your aquarium and then put them into a plugged sink. Add 1/4 cup of bleach for every three gallons of warm water. Do not add any other chemicals.
Let the decorations soak for approximately 15 minutes and no longer. The algae will begin to come off the decorations. Unplug the sink and let the water drain.
Rinse the ornaments with a hose for two hours, according to Instant Reef, to get rid of all the bleach. If all your ornaments will fit, place them in the sink and let the tap rinse them with water. Rotate the decorations periodically to ensure all parts of the decor are rinsed.
How to Bleach Aquarium Decor
Bleach should only be used to clean aquarium decor if the amount of built-up algae becomes excessive. Rinsing and scrubbing the ornaments should normally be enough, but when the decorations become embedded with a thick layer of algae, bleach is a quick solution to brightening you decorations. Bleach can kill your fish, so ensure that your decorations are completely free from the chemical before reinserting them into the aquarium.