cory not doing so well, help!

[mr. pinchers]

ok first the situation. i have a cory thats about maybe 1 yr old. it has not had any prior problems but when i came home today she was swimming in place in one of the corners bobbing up and down to get air. after a good 10 minutes she setteled down to the bottom and hasn't really moved much since. physicly she looks ok EXCEPT for her gills look odd...like theres some kinda piece sticking out. it looks to big to be a parasite though and its not really inflamed. i have a picture that i'm going to post that has a pretty decent shot of the gill. all the other fish includeing the other cory are acting healthy and fine.

http://img507.imageshack.us/img507/1152/corysr1.th.jpg (http://img507.imageshack.us/my.php?image=corysr1.jpg)
(click on the thumbnail for a much better larger image)

i just have done a 50% water change just now and cleaned half the gravel

tank stats BEFORE 50% water change

20 gallon tank
2 mechanical/carbon/bio filters

fish in tank
3 zebra danios
2 corys
1 bushy nose pleco
1 weather loach (dojo loach)
1 checkered barb
2 cherry barbs
1 fish we can't identify looks kinda like a bloodfin tetra but doesn't have red fins, just underside.
various live plants

ok, the various levels in the tank were not ideal before the change

ammonia .50
nitrates - 200+
nitrites - vitually 0
ph about 6.0

weve had the ammonia and nitrites under pretty good control but we can't seem to bring down the nitrates or bring up the PH nomatter what we try

any help with the Cory or the tank is appriciated
-thank

[kimmers318]

ammonia .50
nitrates - 200+
nitrites - vitually 0
ph about 6.0

I am not sure what may be hanging out of the gill of your cory as I don't have much experience with disease (thank goodness) but I can see that you have a serious issue with your tanks water. You should have zero ammonia and nitrites and at least less than 40, closer to 20, nitrates. 200+ is way off the charts if that is true and not a typo which should have read 20+. Either way though, you should not see any ammonia or nitrites in an established aquarium. Are any of these new fish?
Nitrates can only be brought down with water changes. If you nitrates can not be kept under control you have way too many fish in the tank and need to rehome some of them. How often do you do water changes?
Don't worry about bringing up the PH, although a little soft, that is not something to mess with right now. In the future you can try using a substrate specifically designed for increasing water hardness, but if that is what your tap water is you will need to be careful that you aren't swinging the PH down with water changes and then having it swing back up.
The cory could be reacting to high nitrates in the tank and it is causing health issues. Not sure what all health issues you can deal with, but with that high of nitrates I am surprised you aren't seeing more.

[gm72]

200+ nitrAtes???? Holy cow! Water parameters are a mess. You need to do another large water change to get control here. Read through Kimmer's post and give us some answers to her questions so we can help you more.

[SkarloeysMom]

I think that 200+ has got to be a typo. Maybe 20+?

[gm72]

I'm hoping that is the case. Not sure if it is even possible to hit over 200.