It’s impossible to get a true diagnosis for a sick bird, unless you go to a vet. And it has to be an avian or exotic animal veterinarian, or you might still be in the dark.
However, there are a few supplements for bird health that you can use when they’re ill. These products give them energy to fight the illness. They can be vitamins or other substances like herbal ingredients. They will not hurt your bird, when used correctly, but they may save the life of a sick finch.

For example, Morning Bird’s THRIVE is full of high potency vitamins, minerals, amino acids, electrolytes and protein. These help boost the immune system and in turn the bird can fight off disease more readily.

These are products you probably want to keep on hand at all times. Remember, yes they cost money but it’s still cheaper than going to the vet!

Thrive

An alternative to Thrive is Save-a-chick. Use the tiniest amount: Chick Save

HEAT is always a good idea for a sick finch or canary. I like to put the lamp over to one side so they have the option of moving away from it.

Ceramic Heat Bulb

I’m including the next 2 because hygiene is so closely linked with health.

Poop Off

Cage Scrubber

If you prefer, you can DIY an electrolyte solution. Instructions are here. I don’t know how effective these are; I always use the real thing.