Thanks! There are a few big concerns here before we can even consider a possible disease issue. You need to invest in a good liquid test kit such as API fw master test kit asap. If you only set this tank up 7 days ago and you have fish coming to the surface for air, you likely have very high ammonia levels especially with this many fish. The black spots may be the beginnings of ammonia burns but I am not ruling a possible disease issue yet- you need to address water quality issues before even considering any type of treatment. Water quality is a major concern here especially in an uncycled tank.
Ok, here is the bad news. 100l is only 26g of water. If you fill this to the top (120l), its @30g. This is suitable for only 1-2 fancy goldfish with frequent water changes but will likely need to be upgraded as they grow. Six fancy goldfish need a minimum of a 75g tank with 750gph (gallons per hour) filtration. You will need to figure out if you want to keep a 1-2 fancies or upgrade to a much larger tank. The rahpeal honestly needs to be returned. They prefer to be in small groups, require tropical temps not suitable for goldfish and I believe need to be housed in tanks of 45+g (someone please verify if they need more than this!).
Right now until you can get a test kit and figure out your stocking situation, I would start doing 50% water changes 2x a day (one in the am, one in the pm). Make sure you temperature match and properly condition all new water. A good water conditioner such as Prime or Amquel Plus is strongly suggested to help limit toxins between water changes. Ill post some links below with more information- please do not hesitate to ask any questions!!
http://www.aquariumadvice.com/forums/f15/guide-to-starting-a-freshwater-aquarium-186089.html
I just learned about cycling but I already have fish. What now?! - Aquarium Advice
http://www.myaquariumclub.com/goldfish-101-11174823.html