Problem with Corydora

[JD]

First off thanks for the site-lots of info; can't wait to read the e-book.
Also, sorry for the long post ahead!!
Now, I'm a returning student with limited time and funds but still purchased a 20 High for my 8 yr old (first for both of us). The tank has been great except the 2 original zebra danios are attacking the slower corys. We purchased 5 corys after already having 4 danios in the tank. We lost two after the danios continued to nip their fins. A third (aeneus cory) had his tail bit off as well as his upper lip. At first I thought it would be best to put him down but we decided to see how things went. He has healed well, tail is back but lip is gone but he is still eating and swimming as much as he can. Today I noticed his dorsal? (top) fin has been nipped and breathing much faster. Am I torturing this poor fish? The other two corys are fine but are larger than the danios and don't get picked on as much.
NOW, the part you can yell at me for....I have not tested the water ever as my funds have not allowed. I do regular water changes,filter maintenance, and general cleaning (oh and I do add salt as told by LFS but now question it as I've learned some corys can't handle it). I have 2 zebra danios(the crazy killers), 2 gold danios, 4 tetras of some kind(red tail), and 3 corys. All the other fish are happy and healthy! please help if you actually read this entire rant...not sure what is next I can do....

[William]

don't worry about the rant.

You don't need to use salt and I personnaly recommend against it if you keep catfish (such as corys). Salt can help prevent diseases but those diseases is not a problem in a well kept problem. Salt help hide problems which would be better to eliminate.

I will not yell att you since you haven't tested the water. It is good o test to water to help prevent problem but a tank can be maintained without tests.

I am really surised to hear about your aggressive danios. I have never heard of danios that create this type of damage. The fact that they nip fins can be sign that they would prefer to be in a larger school.

[JD]

thanks for the quick response

what would you (or anyone) recommend for the injured cory? will he be OK?
also, will a 20 gal tank handle more fish? the tetras school together well but the danios do seem to stick with the other of it's kind.(2 and 2)

thanks again for your time

[William]

strange danios usually school. The tank could handle a few solitary fish.

Hard to recommend anything for the cory without knowing the water values.