u/ggardensalsasunchip

I started my wet specimen, he’s currently sitting in the formalin. It’s been about a week and a half and now he has dark spots on him. Why is this happening? I was told it could be either due to the metal lid or not injecting him properly. I made sure to inject all parts of him. How can I fix this?? I have a new container that has an airtight glass lid. So I can change it out to that container if that is truly the problem😭 pls help