When did you get the second fish? Do you know what your water parameters are? Even doing water changes once a week you can still get a spike in water conditions. If treatment isn't working it could be ammonia burn.

To answer question how long have I had second goldfish,  the two were in my 29 gal tank for over two years together.  The larger one that has died, I had over three years.  There is only the one in tank, now, the second largest one, and he is now upsidedown...........I switched medication to what they suggested they do for sick fish at Pet Smart, and am using API Melafix  "treats bacterial infections" rapidly repairs damaged fins, ulcers and open wounds......it smells like Tea Tree oil.  This is third day of this new medicine.  Being upsidedown is very bad sign I'm sure, he is still alive.  He is large, about 4" long, and the Fancy Goldfish have a very large body. 

This med says to give for 7 days then do a 25% water change,  the first API med said do a change every 2 days which I did.....I'm going to do another today and not wait the 7 days.   I feel this is all guessing and it's so sad I don't know exactly what to do.  This has gone on for over a week now, but yesterday first day he went upside down

Thank you for trying to help, will get some brine shrimp today.  I did a 50% water change yesterday, and changed to
Mardel brand "Maracyn Two"  which I used in the beginning when there was an infection and had luck with it.  After the 50% water change yesterday I added Nutrafin Cycle which I have always added after water change,  then the new med, first dose was double strength, 2 packets per 10 gal.  now today just one packet per 10 gal. 

He is still upside down, but when I raise him in the net to the top, he is sideways, and skims food off the top.  I don't have brine shrimp yet but will today.  He spit some of the flakes back out, but hopefully kept some inside.  He tried swimming after this, and managed to swim straight for just a few seconds, now has gone upside down again.  As long as there is life, I'm going to try to make him well.  Should I wait the suggested 5 days after this Maracyn treatment to do another water change?  They say 25% change, but would a 50% be better? 

I added aquarium salt yesterday per your suggestion (forgot to mention it) in amt recommended on the box for my 29 gal tank.  When should I do the next large water change?  Yesterday I did 50%, the Maracyn Two treatment is a five day treatment, if I change water before the 5 days won't I lose some important medicine? 
Not familiar with using salt, not sure how much to add again  after the next large water change??? The box states salt stays in the water, and warns not to add more than suggested.

My other suggestion would be to lower the water level in the tank.The reduction in pressure might aid his swimming attempts
If he's eating, then the brineshrimp should clear him of any constipation which might be causing the imbalance.

Have you raised the water temperature, as that might help him fight any infection.


Hope your fish pulls through

Bought a heater today, for 10-30 gal it's a Tetra "no adjusting necessary"  It maintains water at 78   which must be a lot warmer than my goldfish is used to, never used a heater.   Is this going to be too warm for him?   Hope to find your answer soon in case it would be too warm....thanks!

Aww.  So sorry to hear that!  Please don't flush him, though.  If he's still alive, it will make his last moments torture.  Don't give up hope completely, though.  I've seen some fish on the edge just pull through like a miracle, but not all of them do.  Just love him as best you can, whatever the outcome.

Sorry to hear about your fish. If you keep your tank running fishless for a few weeks, any parasites and germs should have cleared.