maybe a bacteria bloom. goldfish create so much waste ur tank probably cant balance itself out. goldfish need about 30 g each fish because they are soooooo messy. i wouldnt use any water clarifier. its just hiding a bigger problem. what type of filter/s are u using and do u have air stones and or a powerhead running?
Sounds like a bacterial bloom, not a big deal, will dissaper soon. But.... the reasons you had the bloom need to be corrected. Whats your feeding schedule like? Maintenance routine? You said you have 2 goldfish in the tank - are you aware that goldies get very large and are big waste producers? This alone may explain the cloudiness. 2 goldies would need a tank of 50 gallons or so...