Fish Are Sick

[ibuyafish]

Hello all.

My fish have been acting off and I have been paying close attention to them and I believe they are beginning to get sick. One reason is my glo-fish's gills are becoming darker and all of my fishes eyes have started to look different, bigger may be the right word for it. Plus my pleco has started to swim to the top, break the water and then quickly swim back down like he's going up for oxygen.

I picked up some API Triple Sulfa and it says to take out the carbon filter. I have a bio-wheel 250, so I was wondering do I take out the carbon filter cartridge all together or should I cut the backing off of the filter to take the carbon out and leave the mesh filter. My filter has a wheel (bio-wheel) that always stays in there and is never changed, and then the carbon filter pad that is changed every two weeks or so. But is it okay just to run the wheel without the carbon filter while I use the medication?

Here is my tank status:

PH 7.4
NO[sub]2[/sub] 0
NO[sub]3[/sub] 0
GH 4[sup]o[/sup]dH
KH 0[sup]o[/sup]dH
NH[sub]3[/sub]/NH[sub]4[/sub]+ 0
TEMP: 76.4[sup]o[/sup]F
TANK: 20 U.S. Gallons
STOCK: 6 Neon Tetras, 1 Black Skirted Tetra, 2 Glo-Fish, 1 Pleco

 

[spectrum]

No nitrates is unusual, you have cycled it right? The pleco swimming to the top sounds exactly like he's going for oxygen, is the filter outlet breaking the surface?
Never experienced it myself but I think that sounds a bit like Dropsy
Yes it is OK to run the filter without the carbon, carbon is not necessary, its actually good at removing oxygen! Take it out, that could be the issue.
Hope this helps

EDIT* What sort of Pleco is it?