High nitrate

Test results? High nitrates seldom cause a problem for fish over the short term. High nitrites or ammonia could cause some of the symptoms you've described, and based on the age of the tank, would be my first guess. How often do you do water changes? Filtration?

I would do 50% water changes daily, myself. Also, you need to look into investing in a good testing kit(s). I suggest a Master Test Kit for Freshwater so you'll have access to many tests. You need at least ammonia, nitrite, nitrate, pH and I recommend also gH, kH, and phosphate.

Also, did your aquatic store sell you all of those fish knowing they were going into a 60L tank? That tank is way too small for those fish. 60L is just under 16 US Gallons. None of the living fish you have listed can live to adult size in that tank.

First things first, your fish are going to grow much larger than the tank that you have.

What are your water parameters? pH, ammonia, nitrites would be extremely helpful, as high nitrates (even 40 ppm) will not usually give the symptoms you described whereas even low amounts of ammonia or nitrites (1 ppm) could cause fish fatality.

In a 75L tank (~20 USG) you could do a variety of small tropical fish. The best question is not what fish I would recommend. The best question is what type of fish do you like, and then research to see what sorts of living conditions they require. If you can provide it for them, congratulations, you've found a fish to keep.

I suggest you start here. That is the link to the Species Profile section of Aquaria Central and it has fish and lists what tank size they need. You will want nothing listed over 20 gallons for a 75 litre tank.

If you are asking me what I would put into my own 20 gallon, I can answer that easily, as I have been researching and getting ready to set one up. I want a 20 gallon long, planted with low light plants, no CO2 injection, an RFUGF and a small sponge filter. In it I will place two trios of Endler's Livebearer's, a couple of Coryadoras Catfish, two otocinculus catfish and then let the Endler's get busy. I like Endler's because they are small, ultra-colorful and easy to breed. There is some speculation that they may also be extinct in the wild now as well, so I'd like a shot at keeping the gene pool more broken up by at least getting my own group going and then trading with other Endler's keepers down the road to see what we can do for these little guys.

So you see, it's best to do some research and find out what you wish to do on your own. If you have questions, you can always ask here on the boards about compatability. Most important rule of all is have fun and enjoy what you are doing. You will be happier and you will keep your fish happier, and really, I think that is what this board is all about.

Great post, Harlock! I as a newbie ready to set up a 20g myself have received so much advise about what everyone else would stock and I have discovered the only one who will be happy w/what is stocked would be me and my decisions.

Don't get me wrong, I have loved the advise of what not to put together after I have mentioned it.

Question though, what is a Endler's Livebearers? I know what a livebearer it but an Endler's?

My stock idea for my 20g:

2 dwarf neon gourami
10 or so cardinal tetras
3 dwarf spotted cory

Currently have a 2 1/2g w/male betta and two dwarf spotted cories. They are getting along swimmingly!

Endler's Livebearer is a cute little fish. The males are just under an inch to one inch in length. They can breed with guppies producing infertile offspring. They look like this:

There is a link about them here.