Thank you, I guess I should post a picture so you can see what I see. that would probably help. I will take one tonight with the lights off in the room so that it will be easier to see the tank instead of the it's surroundings.
I'm asking questions to try to help you. You can have 40yrs of "experience" and still be doing things improperly.
If you rinsed the entire contents of your tank in chlorinated tap water, you wiped out most, if not all your beneficial bacteria. This will cause water parameter issues and can cause cloudiness. Doesn't matter if you've been doing it this way for 15yrs. It's how this works. Could you have gotten by without issues? Absolutely. But it's unlikely.
You could also have an algae or diatom bloom going on. One female guppy having a batch of fry in a 50g tank almost certainly did not cause this.
I wish you luck.