I'm a new owner of a goldfish tank and need help

[Santana]

I recently got a new filter system and I noticed my fish are swimming around side ways upwards fast like there dancing I don't know if that's a good sign or bad because I never seen them act like this and when I go up to the tank they all come to me fast like there happy or are they trying to tell me something different

 

[Aiken Drum]

Do you know your water parameters? pH, ammonia, nitrite and nitrate? If not take a cupfull of water to test later, and either get a test kit like API Freshwater Master Test Kit and test the sample of water you took, or take the sample to a fish store where they should be able to do the test for you. Write the numbers down and report back. Once you have taken your water sample, change 50% of the water.

How did you change your filter system? Did you reuse your old filter media in your new filter to maintain your cycle?

How old are these fish? They look like babies from the photos. What size is your aquarium? What filtration do you now have? How many goldfish are we talking about in there?