I recently got given a two gallon fish tank and five fancy goldfish! (birthday present)
After a quick google I realised that this tank is completely unsuitable and managed to get a second hand 4ft fish tank I've estimated it holds about 30 gallons. To find out this still isn't big enough and now to too it off two of my fish have White spots on their fins! My question is really how do I get rid of White spot and how long will my fish tank be suitable for 5 goldfish?
I have live plants and a filter

To answer the question regarding how long the fish will be OK for in the 4-footer: maybe a few months before they'll need to be moved.

Whitespot (also called Ick or Ich) is a disease that needs to be tackled early to cure it successfully. Poor water quality is a main cause of disease; in particular high levels of ammonia and/or nitrite. I'd recommend testing the water to assess any potential problems that might need addressing by carrying out water changes before you start dosing chemical treatments.

When it comes to treatment, people often have differing opinions on how this should be carried out. Increasing the water temperature to around 30°C is known to speed up the life-cycle of the parasite that causes whitespot, aiding treatment.

However, increasing the water temperature can also have detrimental effects of its own. The warmer water gets, the less oxygen it can hold which can result in a deficiency and unhappy or potentially dead fish. Increasing surface agitation from the filter and adding at least one airstone to the aquarium will help to maintain the level of dissolved oxygen.

Many fishkeepers swear by the use of salt, however I'm more skeptical. Adding salt obviously increases the salinity of the water which can place more stress on fish that are already diseased. The fact is, most freshwater fish simply can't tolerate saline conditions. Instead, I'd advise a chemical medication such as eSHA Labs Exit dosed according to the manufacturer's instructions.

Finally, it is imperative that you maintain good water conditions. This means no detectable ammonia or nitrite, a stable pH level and ideally, a minimal nitrate level.