Welcome to AA:
AG was kidding when he said it was a 12-step program, it's actually three. This may have caused the problem:
I just gave the aquarium a very good cleaning a few days ago and it looked beautiful
A "good cleaning" sounds like you cleaned the filter, decorations and gave it a good gravel vac. It looks like you disturbed the beneficial bacteria colonies in the filter and gravel. This is normal and will settle shortly. If the above is not the case, something else caused the issue.
How long has the tank been set up?