Pygmy Cory Swimming Problem!

[showjyr]

One of my three pygmy Corys is having a lot of difficulty swimming. It doesn't seem to have any injuries but cannot swim upright. It has plenty of energy and all but swims in....well kindof a spiral, like a plane going down.

What could it be?

 

[*Fishkies*]

What are your water parameters?
How long has your tank been setup?
What size is your tank?
How many fish and what kinds of fish are in the tank?

How often do you do water changes?

 

[showjyr]

What are your water parameters?
How long has your tank been setup?
What size is your tank?
How many fish and what kinds of fish are in the tank?

How often do you do water changes?

Haven't tested in a long time but always have been spot on...it's heavily planted.

Around a year.

30 gal

6 otos, 4 peppered corys(just had some babies), 5 endlers(2 pregnant), 3 pygmy corys, 6 cajun dwarf crays, 20 or so cherry shrimp.

30% weekly water change.