If you want to save your fish, the first thing you need to do is to get tanks of proper size.
Those fantails are fancy goldfish, and their requirement for tank size is huge. We recommend no less than 20 gallon for just one, then at least extra 10 gallon for each additional. You need a
55 gallon and a highly efficient filter system to sustain them. The 4 gallon is the killer here. There is nothing you can do to keep these 4 goldfish alive if you don't upgrade the tank.
The same goes for your guppies. Although they do not need nearly as big of a tank. A 10~15 gallon should be fine for 7 guppies for now, but these livebearers will breed fast and overstock your tank later.
Until your tank is cycled, your fish is always under the risk of dying to ammonia poisoning. Aside the partial water change with Prime on daily basis until your tank is cycled, the other thing you can do is try to speed up the cycling. Some of the things you can do to help the cycling go faster are,
1. Increase aeration
More oxygen will help the beneficial bacteria grow faster in your filter system. You can achieve this by adding more air stones connected to your air pump.
2. Raise the water temperature
Nitrogen cycle bacteria love warmer water. They will grow faster and convert ammonia faster if you can slowly raise the water temperature to low 80F.
3. Heavy bacteria seeding
One of the fastest way to help cycling a tank is to heavily seed the tank with nitrogen cycle bacterias. Get a bottle of
Tetra SafeStart will help jump start the cycling even if it doesn't get your tank cycled right away.
You can find these tips for cycling in
this article. The article is about fishless cycling, but the tips are the same for cycle with fish.
