I was feeding my betta in mine, and I had a lot of white mold on mine so I rinsed it really well and it was slimey and then some paint flaked off. I stopped feeding in it and now I use it as a baffle on my filter LOL.. but yeah, take it back to the store if you can, maybe exchange for a new one? I've heard some people say the paint flakes.
I have an aztec head from petco from years back. Scrubbing the algea off it in the sink flaked off some paint, but never in the tank. Don't be surprised if some paint flakes off when you scrub it, but it's not really noticeable since the stuff it's made out of is dark colored.