i also wish i could find an easier way of removing the backing of the cuttle bone. chipping it off with a knife is such a pain... it takes forever and seems to be messy (of course everything i do seems to be messy)! but to answer the first persons post... i think that the cuttle bone would be safe for all the turtles, it just adds calcium to their diet. (i cant see why it wouldnt be good for the other turtles if it's ok for the RES)... also, i break mine into pieces, and i replace it whenever that piece disappears from the water. either it dissolves or they eat it. but dont worry, if it dissolves, they get the calcium through the water, so it's not wasted if they dont eat it. well i guess that's all, just wanted to add my 2 cents... hope it helps 
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~ Evie 
Pets:
German Shephard {Dusty}
German Shephard/Collie mix {Shadoe}
2 RES turtles {Booger and Snot}
African Clawed Frog {Bingo}
Snail {Gary}