I have 3 corys (probably Corydoras venezuelanus). I've had them and they've been together since Feb. 5, 2007. One of them recently lost his coloring: at first I thought it was a trick of the light, but he really has lost the green patches on his shoulders so that he's almost all beige. The other 2 are fine. All 3 are acting normal, even the pale one. They've never been separated.
I did move them to a new tank one month ago (June 24), but I moved them with mature gravel and decorations so have never had any problems with ammonia, nitrites or nitrates. They're currently in a 10-gallon with gravel; tank mates are 3 guppies & 1 ghost shrimp; there is an underground filter and a power filter.
I vacuum and change 10-20% of the water generally once a week. The water parameters that follow are from today, 10 days after my last water change:
- pH 6.4-6.8 (between those 2 colors on the strip)
- Alkalinity 80
- Hardness 120
- Ammonia 0
- Nitrite 0
- Nitrate 40 (this is higher than usual because it's been 10 days)
I haven't used any medications. I can't find any diseases that match his symptom. Like I said, he's acting normal, hiding when he sees me, eating when he thinks I'm gone.
The only environmental conditions that have changed that I can think of are:
1. Temperature: moving from downstairs 78-F to upstairs where it got as high as 84-F a couple days last month (our house isn't air conditioned), but it was a gradual change as the room temperature changed; mostly the temperature has been around 80-F.
2. Water conditioner: I switched to Wardley 3 in 1 to buffer pH in addition to removing clorine/chloramines.
3. Tank mates: Previous tank mates were danios, oto cats and frogs; the guppies are new, but I think they're fine.
