Cleaning Rocks And Corel

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I have been giving my tank a good clean. Ive cleaned the plastic and resin ornaments with bleach and they have come up good. I have 2 rocks and 2 pieces of corel that need cleaning, I dont fancy using bleach on them as I dont know how porus they are. Ive tried scrubbing with a tooth brush, Boiling water with loads of salt and a scrubing brush, The algae isnt shifting. Any suggestions???