I think you're right. I recall someone using a credit card too. Only, I'm not sure it was used on an acrylic tank either. Seems like it would be but better be certain b4 you try it. Try a search using credit card, maybe that will find it?
Yup, it did. John Miller reported doing so in a thread a while back. If I knew how to copy and paste the thread, I could put the link here. Just use the search button in upper right corner, you'll find it.