In my 55 gallon, I have a few basic plant pots which I have partially buried into my sand to make caves (I boiled them for thirty minutes before adding them). One of them is a medium sized pot which I broke in half to sort of suit my needs. I have since decided I don't want that one in my tank, and I am donating it to my sister. She, however, wants to paint it to match her decor. Is there any safe paint we can use? Or a safe sealant of sorts? I'm assuming my canvas acrylic paint is not safe, nor would be my varnish.