Yup, you've got destructo-turtles

When I first got Ralph live plants, that exactly what he did. But now, he's developed a taste for them and eats it all in 15 minutes

I buy the potted ones, because every so often I can get them for 3 for the price of 1. Once he's eaten it down to the nubs, I put it in a little 2 gal tank, with 2 feeders I saved, and now a rather large colony of snails (At least 4 of the snails are bigger than the fish!). I let the plant re-grow, then give it to him again. Although, he hasn't got any since the snails starting going nuts and I found 4 snails in the filter last time I gave him a plant :/