Removing Gunge From Rocks

[LauraFrog]

I'm setting up a micro paludarium in a 6 gallon tank I've had lying around... its internal filtration system is utterly bummed so I wanted to do something interesting with it that doesn't require that system.
I went down to the creek today to fetch some rock. (I always use rock from this creek, I have it in every single tank I own, utterly inert, never had a problem with it as long as I rinse it first.)
These pieces are covered in a few years worth of baked on silt. Normally I just shove them in anyway, but I'm not keen on doing this because I've got to silicone them in place for this tank. If the silicone sticks to the silt and not the rock, and later the silt falls off, my complicated rockwork will collapse and smash the tank. Not pretty.

So can anybody think of a way to shift all this crud? I scrubbed at it for about half an hour with cold water and elbow grease and I couldn't get it off. Is there any cleaning product that will somehow get it off, that can be reliably removed afterwards and not kill all my fish?

 

[drobbyb]

Did you try a wire brush?

 

[lordofthesea]

try vinegar. if it's calcareous, it'll dissolve it. if not, chip it off and stick those bits with silicone as they will be rough with no gunge

 

[bae1994]

jet wash it (power washer it)

 

[matalan]

jet wash it (power washer it)

Scrub a Dub dub + pour Boil water over it.

 

[bagu]

like matalan said...

boil it till its bubbling then a bit of elbow grease =]

 

[Infidel_Uk]

hi power steam clean gets my vote...

 

[LauraFrog]

Thanks guys! Tried wire and nylon brushes but didn't think of hot water or vinegar, might try that next. Failing that the chipping sounds like a good last resort. I'd like to avoid it because this kind of rock tends to split along pre-existing fault lines, and ruin your nicely shaped pieces.