I've used a bathtub scrubber brush in the past with no ill effects. I was sure to keep the rock in a bath of salt water while I cleaned. It cuts down on the mess. I did it during a water change, so I had lots of tank water for this purpose, that got thrown out after use.
One thing, if you're going to use a toothbrush, just don't use whitening toothpaste, it will bleach out the coralline! 
_________
90G display tank. Kent Phos Reactor running carbon and ROWAPhos, Coralife 225 Skimmer, Typhoon 5 Stage RO/DI, 20 Gal Sump/Refugium with Chaeto/Caulerpa lit opposite daylight cycle. Coralife 2x150MH, 14K + 2x96W PC Actinics, Ecotech Vortech propeller pump, Hydor Koralia #2. |