Hi can you help one of our goldfish is struggling to swim , he seems to struggle to get horizontal infact he is almost vertical all the time and when not swimming like this he will sink to the bottom.Then come back up to the surface and gulp for air,

WATER CONDITIONS UNKNOWN
TANK SIZE APPROX 3 GALLON,ON THE GO FOR THE LAST 4 WEEKS
FILTER NONE
1ST WATER CHANGE END OF 4TH WEEK
HOW MUCH APPROX HALF
FISH TWO NUMBER
SIZE APPROX 2 1/2 INCHES
WATER ADDITIVES BIO ACTIVE TAPSAFE
MEDICATIONS NONE
NEW FISH NONE
FISHFOOD KING BRITISH GOLDFISH FOOD
SIGNS OF DISEASE NONE
RECENTLY REMOVED SOME ELDEA PLANTS THAT WHERE DYING

Hello Tomy Mac & welcome to kokos!

There is good & bad news.

Good news : Very excellent of you to take the pre-emptive and answered the questions in the white box above, which saves us a lot of time addressing the problem.

Bad news : From the info you gave us, it's clear that you fish has been living in, shall I say, "less than ideal" conditions. An ideal tank for two goldfish is at least 20 gallons in volume, have a filter with at least 200 gph, adequate aeration, and (usually) at least once a week routine waterchange.
Your water parameters, I have no doubt, will be toxic for your fish.

What you gotta do ASAP: Do a 90-100% waterchange now, and make sure to acclimatise the two fish to the new water SLOWLY. Get a bigger tank of at least 20 gallons as soon as possible. Get a filter that pumps 200 gph. Don't buy anymore fish. And read the links below:
http://www.kokosgoldfish.com/tensteps.html
http://www.kokosgoldfish.com/cycle.html
http://www.kokosgoldfish.com/care.html
http://www.kokosgoldfish.com/Filtration.html

I know this is a lot of things to do, but they're all essential to ensure the survival of your fish.

Once again welcome and keep us updated!