Mystery death?

[dafishman]

Okay. So, here's the basics.

I have a colony of 6 Neolamprologus multifasciatus.

Tank Size: 10g
Ammonia: 0
Nitrites: 0
Nitrates: High, at 50+ ppm

The problem is, I lost one of the multies today. When I found the fish, the mouth was gaping unnaturally wide. Also no outward signs of trauma, apart from one fin that was slightly frayed.

Tank has plenty of water circulation and surface agitation, so it's not lack of oxygen that I can figure. Due to high nitrates, I have a lot of algae growth.

The fish were not eating well yesterday (usually greedy little buggers) and today I topped off the evaporated water with fresh, not wanting to shock them by a large and sudden water change, I was opting to first add water and then in a day or so do a wc, so as not to cause undue stress (my water changes have not been as regular as I like.) This has been the only change in the last several weeks. Nothing new has been added or removed.

Also, the other fish appear to be breathing a little more heavily than normal, and are hiding more than normal, appearing sluggish and, as I said before, mostly unresponsive to food that, two days ago, they were devouring.

What am I dealing with here, any idea?

 

[shaynablizard]

Although tanyikans can be sensitive to large water changes, I would still do a 15% water change. Make sure the water is exactly the same temp, and have it conditioned prior to adding it to the tank and they should handle it fine. While it's possible that one fish had a medical issue that isn't related to the water, but the fact that the others aren't acting normal concerns me. I'd probably continue to do about 10% water changes daily and feed in small amounts. Maybe try to tempt them with live microworms, brine shrimp, or something like that.
Although nitrates are tolerated well, yours are very high and I think these water changes are very important as well as not overfeeding. Wouldn't hurt to wipe out some of the algae growth and clean the tank up a bit when the fish stabilize.