Please help me check my nano tank.

[TheNewClownFish]

Hi everyone. I bought a used Red Sea nano (18.5G) on marketplace. When I brought it home, I noticed this on the silicone. I’m hoping it’s cosmetic.

It’s currently filled with fresh water (hence the bubbles) as I’m doing a leak test.

Thanks.

 

[TheNewClownFish]

Another photo for more assessment! Thank you.