Mystery problems with tank/fish

[sliderfish]

A friend of mine's tank has been experiencing a few problems lately and I've run out of ideas. The tank has been set up for over a year. When he added some new fish to the tank roughly two months ago they (old and new) started dying. His nitrates have been high and PWC's have not helped it go down. He has noted red gills on some fish, but many seem to have no symptoms and are dead in the morning. My guess was ammonia, but that doesn't seem to be it. Any ideas, information or suggestions are welcome and encouraged. Thanks.

His tank is a 20 gal and his current stock is a guppie, a CAE, a neon, three mollies and another small tetra. His stocking levels never reached 15 fish at any time and the fish types have been consistent. I have taken a picture of one molly that shows red gills and he is the only current fish to show any symptoms.

 

[StuG]

When he added some new fish to the tank roughly two months ago they (old and new) started dying.

I would imagine that's your biggest clue right there. Were the new fish quarantined before being added to the tank?
I would have thought Ammonia too, but you checked for that. With it happening when new fish were added perhaps it's a bacterial thing?

 

[sliderfish]

They were not quarantined before being added. He didn't know he needed to do so. And yes that is the best lead I have (the new fish)...

 

[roadmaster]

A friend of mine's tank has been experiencing a few problems lately and I've run out of ideas. The tank has been set up for over a year. When he added some new fish to the tank roughly two months ago they (old and new) started dying. His nitrates have been high and PWC's have not helped it go down. He has noted red gills on some fish, but many seem to have no symptoms and are dead in the morning. My guess was ammonia, but that doesn't seem to be it. Any ideas, information or suggestions are welcome and encouraged. Thanks.

His tank is a 20 gal and his current stock is a guppie, a CAE, a neon, three mollies and another small tetra. His stocking levels never reached 15 fish at any time and the fish types have been consistent. I have taken a picture of one molly that shows red gills and he is the only current fish to show any symptoms.

Would maybe test the tapwater for nitrates and if levels are zero or low, then perhaps I might get aggressive with gravel vaccum and reduce feedings as well until nitrate levels were lowered.
Would note that mollies and guppies prefer hard alkaline water that tetras don't enjoy in the long run, and that the mollies and guppies also prefer warmer water than neons and many other tetras do best in long term.
Sure they may tolerate the enviornment but are often stressed when kept this way for extended period and some become sick and or die in weeks,or months.
Have kept mollies and guppies as mentioned in hard alakine water with pH between 7.5 and 8.0 with 10 to 15 dgh and temp between 80 and 84 degrees F.
Tetras I have kept with exception of cardinals and rummy nose all did much better in cooler water with temp between 75 and 78 degrees F in the long term, and pH values between 6.8 and 7.4 and fairly soft to moderatley hard.
High nitrAtes are often indication of excess organics which could be result of dead plant material,decaying food in substrate,excess waste from fishes,waste from snails,etc. Gravel vaccuming one third to one half the tank during weekly water change and different area each week can reduce nitrate levels. Just my two cents.

 

[dkpate]

Try doing a good gravel vac and swishing the filter media in old tank water, and see if that makes you nitrates go down. What ppm are they at right now? What are you using to test the water?