Can anyone help diagnose my silver dollar problem?

If you want to get some help, you must be willing to listen to more experienced fish keepers' advice.

The bottom line is your tank is overstocked and unless you accept pieces of advice posted here, your fish will keep suffering.

What are your water parameters?
 
Trying not to get you mad, but......

Two years ago your tank may not have been over-stocked (fish was smaller). It is now way-over-stocked.

Sorry...
 
Silver dollars get big and active and are schoolers. Tiger barbs also school. The dino eel needs about 55g min. and puffers are bad community fish. So your tank is overstocked.. and the puffers definitely need a new tank. Neon puffers are dwarf puffers, right? You could set up a 10g for them.
 
I have no clue what neon puffers are, but all puffers are agressive especially when cramped like the way you have cramped them. Your eel will easily outgrow that tank, and IMO silver dollars belong in a 35..... Just because the fish physically fit doesnt mean that they are thriving and living correctly.

An AQUARIUM SALT dip, not a MARINE salt dip would help the fish as mentioned before. I bet you could sell your eel or buy a 55 gallon tank for him (on craigslist for about a hundred bucks) easily.

Tiger barbs and silver dollars are inactive and tend to hide when not kept in a school, and them hiding in the corner is probobly due to lack of oxygen and poor water quality.
 
Neon puffers are dwarf puffers, right? You could set up a 10g for them.

Some research has shown me, that they indeed are dwarf puffers. They prefer having snails in their diet, and a good rule of thumb is to have 1 puffer for every 5 gallons. A ten gallon tank with 2 dwarf puffers and a few otto catfish and ghost or cherry shrimp would be cool, just make sure to provide TONS of plants for the puffers, because bordom causes them to KILL
 
oh, could you please show us a picture of your tank, and the silver dollar thats injured?
 
poor fishies
 
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