In retrospect, using a weight as a icon for strength when fish weighing a certain amount was probably not the wisest. I changed the sprite to better indicate that it is upgrading strength. I also made it so you need strength earlier since the rate at which you gained strength made it so you never noticed you couldn't remove a scale in one click.
Turns out, being inconsistent in how you are naming things in code really messes things up. The gold purchase buttons should work now. I also fixed the bug where the buy buttons never went back to grey if you couldn't afford them.