Is this lime scale? Can it hurt the frogs and how do I get rid of it without harsh cleaners?

[shydroanna]

My terrarium is growing/getting some hard scale deposits that I assume are from hard water? Is this correct? Is so ho do I clean them off without using something that will harm the frogs? Is there a way to prevent this? I use tap water with tap water conditioner when adding water and calcium supplements every 3rd feeding or so.