If you're looking for the most reliable way to get the software, I can direct you to the official site. Or, if you're experiencing issues with a legitimately purchased version, let me know the error code!

The safest place to download is the developer's official site at SimAquarium.com.

The Steam platform hosts numerous affordable, modern virtual aquariums (like Behind Glass: Aquarium Simulator or Biotope ) which frequently go on sale for just a few dollars.