More filtration for sure. The cloudy water could even be a bacteria bloom trying to compensate for lack of breeding grounds. Did anyone mention a 40 breeder is really too small for 3 goldfish long term? You want a bare minimum of 20g per GF, 30g per is better though. They are BIG waste producers and you will find yourself fighting these kinds of battles often with an overstocked GF tank.
You don't need that all you need is some prime and when you add new fish add dr tims live bacteria that's all I've been doing for the past 6 years and still have 2 original fish
I agree with FreshyFish. Goldfish require maximum filtration.
I'm not a fan of adding chemicals to the tank, however, including all those you mentioned.
And as Tanker said, Water changes, water changes, water changes, and lots of biological media in the filter(s)