Madelein,
As for the tank, it is a one foot tank which has been running for ± 1 month.
It sounds like you have a small tank housing 4 goldfish while trying to cycle. Your 4 fish need to be in a much larger tank.
IMO, until you know what your water readings are, I would feed them only once a day, with 10% water changes everyday.
As for getting your tropical tank, I would recommend that you get the biggest tank you can afford. At least a 20 gallon. And I would recommend that you research about the Nitrogen Cycle. If you have any questions, come post them here.
I don't have a lot of experience with goldfish, but I do have a great article that a good friend wrote that might help you out.
SWIMBLADDER DISORDERS
Caused by:
Various factors including temperature changes, although other factors, such as microbial infection may be involved in some instances.
Obvious Symptoms:
Although an infected fish usually appears in reasonable condition, it experiences difficulty in maintaining its position in the water. It may show a list to one side, for example, or even float on its side or back at the water surface or remain sunk on the bottom of the tank or pond.
Occurrence of the Disease;
Simmbladder disorders may occur in a variety of situations, often spontaneously in previously healthy stock. Other fish in the same pond or aquarium may remain unaffected. Certain Fancy varieties of goldfish, such as moors, veiltails and orandas, are particularly prone to this condition and often have misshapen swimbladders.
Treatment and Control:
Since the exact causes of this problem are poorly understood, recommending a reliable treatment is difficult. Air-gulping occurs when fish feed greedily at the surface and suck in air with the food. One solution is to briefly hold the food just beneath the water surface so it quickly sinks when released and has to be eaten in midwater. If the buoyancy problem is not due to air-gulping, then it could be a more serious condition affecting the swimbladder. Try moving the fish to shallow water, say 13cm (5in.) depth. In the case of goldfish and other coldwater fish, slowly increasing the water temperature by 5C (9F) sometimes brings about an improvement. Dosing the tank with an antibacterial remedy and/or aquarium salt (up to 1 gm of salt per litre, assuming the fish are salt tolerant) may be effective in some cases. Despite attempts at treatment many cases of swimbladder problem fail to improve. If the affected fish seems very distressed or is unwilling or unable to feed then it might be kinder to put it down.
