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Hello,

Here are the parameters of my tank, as measured just now:

Size: 20 gal tall
Pop: 3 neon tetras, 5 bronze corys, 2 upside down catfish
(all of the fish have been in the tank either their whole life or at least 2 years, except 2 neons, which I added to the tank 3 months ago)
Strata: small gravel
Plants: two swordtail plants
Other: two "fake" rocks/caves

pH: 6.0
Ammonia: 0 ppm
Nitrites: 0 pmm
Nitrates: 30 ppm
KH: 1 or 2 degrees (so, less than 50 ppm)
GH: 3 degrees (about 50 ppm)
temp: 82-83 degrees
water change: ~30% every 10 days

The reason I am writing is because last night I noticed that one of my two Synodontis nigriventris (from here on I'm just going to refer to them as upside down catfish) has a huge white splotch on her/his underside. I was away for a month, and my husband didn't notice it while I was gone, so I'm not sure how long it has been there. It doesn't look like a growth, or like it has any texture at all. It simply looks like there's a big spot on her underside that has lost all its color.
Has anyone heard of this happening before? Now, my tank has seemed pretty healthy for awhile, and honestly, I hadn't been testing the water for some time. I just ran all those tests now, and was pretty surprised about how low the pH was, how high the nitrates were, and how soft the water is. Anyone have opinions about that? The fish have all seemed quite happy, and the tank "looks" good (ie: clear water). For awhile I had a fair amount of green algae growth, but I'm pretty sure it had to do with too much sunlight hitting the tank. We've closed the curtains of the nearby window lately and its really help cut down on the algae growth.
So, I guess to recap, my main question is about the upside down catfish, but if anyone has any insights about the rest of the parameters, I'd love to know about them.

Thanks so much,
Sarah

Do you have a heater in there? Sounds like it might be a heater burn.

Hi there...

I do have a heater, but I've never seen any of the fish even get close to it before. It is in the upper right hand back corner of the tank. Also, it doesn't seem to be very warm to the touch. Do you still think that might be the cause?

Thanks,
Sarah

It's actually hard to tell without a picture.

I can appreciate that. Unfortunately for me, I rarely see these guys, and my camera doesn't do well when I've tried to take other tank pictures. I guess the best I can do is describe in words. Sorry!

Thanks,
Sarah

You might want to search the forums for "heater burn(s)" and see if any of the pictures diagnosed as such match the condition in your fish.