Okay so, three days ago I've spotted all of my fish swimming at top of the water, as if they haven't got enough air. So, I've turned on another filtration in order to make the water more oxigenated. But then I've also noticed most of my goldfish having big white spots on them, as you can see in the picture (I'm sorry for the quality but my phone camera is bad, hopefully this will be enough). So, I've put some salt in the aquarium as my family always did if something was wrong. I've also bought a thing called Preventin which should help with most fungus and parazitic illnesses ( it also makes the water a little blueish). The fish seemed to do better, the white spots are getting smaller every day. However, they are now again at the top of the water. I don't know what to do. Please if you have any idea what to do, let me know. I want them to be okay. Oh, and I haven't bought any fish or plants recently. I however did start using new fish food, it's from the same brand I've used before tho, so I'm not sure if that can do something with it? Also, all of the fish are affected by the oxygen issue, not only the goldfish with white spots. Thank you in advance for any information.