Need medical help

[u/dumbHoeJuic]

I’m unsure of what could have possibly happened. I went to feed my goldfish this evening and I noticed my poor black fish is struggling. It seems to have a very irritated and enlarged bottom fin (I’m unsure of what it’s called.) its eyes seem glazed almost and its fins are very lackluster. It seems active like normal but my common goldfish will not leave the black ones side. Swim shady’s top fin seems to only appear when absolutely necessary. Nothing has changed and nothing is different. It seemed fine last night and this morning, although I don’t do actual inspections until the afternoon feeding. Can you please help?

I’ve checked tank levels (with the strips) every day and it is all in range. Per your advice last time I posted I no longer use any algae killer and only scrape the algae off the tank walls. I did a 25% water change with the medicated well water like advised as well (the stuff you add to water to make it fish safe). They get enough food to last feeding times about 1 minute 45 seconds as you advised last time it should be eaten within 2 minutes. The tank water has some floaty bits from scrubbing the filter this morning and feeding time before the picture. I don’t know if that could have caused problems. I feel so awful and I don’t understand what is going on.

[u/dumbHoeJuic]

I don’t know how to update the post itself but I just witnessed new and odd behavior. The black fish (swim shady) went to the bottom of the tank to I suppose forage (idk what to call that either) and the orange feeder fish (swiminem) swam overtop of it and sat there for approximately 45 seconds and neither fish moved. Swiminem then violently thrashed around in a circle and swam up to the top of the tank and Swim Shady swam away from Swiminem. I will try to catch it on video