Since your tank is relatively new, this could be a water quality issue. Do you know what the water parameters are (ammonia, nitrite, nitrate)? Goldfish create ammonia by simply being alive (respiration , wastes, ....)..Do a complete water test first. If the readings are too high, then perform frequent partial water changes to bring them down to a safe level.

How big is your tank?

They are poisoning themselves by breathing in this tank, it's too small even for half a goldfish, let alone TWO and Orandas on top of that! Did you know that they can grow to be close to 30cm long?

Buy a new tank, a 30 gallon (or something like 150L) for these two fish. Buy a test kit, with ammonia, nitrite and nitrate. Funny enough, pH couldn't matter much less right now to you, so please start doing something asap!!
When you get the new tank, add water and let it stand for a day before you add the fish. Get yourself some fluid beneficial bacteria, in this case I'd strongly recommend "fluid filter media" by Easy Life, this will help and support the fish to recover from their burns. If you can't find it, buy "Stability", by Seachem.

Hurry hurry!!

Starting to go black at the edge of fins = AMMONIA BURN !

DANGER ! Your fish are poisoning themselves and will die if you don't do anything

ASAP to do:

Get a testkit: MasterTestKit for freshwater by API . While you get down to the petshop take a water sample ( half a cup full ) with you so they can test the water asap. Please post the numerical results.

Get a much bigger tank: 30 gal at least, 40 gal better.   
Get STABILITY by Seachem
Get PRIME by Seachem
Get Pimafix AND Melafix by API         
Get a very good filter, a pump and an airstone.
Get live plants and plenty of gravel ( best the natural, round, peasized one, instead of the artificial coloured one - avoid any sharp edges)

Set up the tank ASAP and add Stability and Prime according to instructions.

In the meantime do 50% waterchanges every day in the small tank but please add the conditioner to remove chlorine and chloramine and add the beneficial bacteria. VERY IMPORTANT.

G O O D    L U C K

I keep fingers crossed your fishies make it, as this is really EMERGENCY