I agree. I once painted the outside of my tank (for a background), using black acrylic, and I had to air out the room this was done in because the smell of chemicals was too strong. I cannot imagine it being inside a fish tank. It would also most likely dissolve in water.
Acrylics are aquarium safe but you do have to seal it with an aquarium safe epoxy. If you do some research or check out King of DIY on YouTube, there is a lot of info on painting /making decorations. Be sure to let it air dry a few days/week before using in aquarium.
Personally, I have used krylon fusion spray paint in the past with no issues. I have also used drylok coated with spray paint and then sealed it with epoxy with no issue.
I would definitely avoid from using that inside the tank, as acrylic is a water-based paint. It'd definitely dissolve very quickly, and harm the fish. However, it's totally safe to paint on the outside, which is what I'd recommend.
I have used:
Krylon Fusion (discontinued by Krylon)
Acrylic Craft paint for 3D backgrounds
Plastidip for PVC weirs and spray bars
Rustoleum Textured paint for 3d backgrounds
Polyurethane spray for 3D backgrounds
2 part epoxy Sherwin Williams black paint
All inside tanks all fish safe all low VOC no issues.