Not a whole lot of comments about the fish. However, I am still going to post this. A step by step guide to the aquarium. Follow this guide and you should not kill anything.
First, what I have is an Eclipse System Six. You can get these things for around $50. Now normally I would not have selected this type of setup, but it was for a small office and compactness was a major deal. I had to do some manner of work after all. Taking up all the desk space with the aquarium would have been very possible, but it would also have killed the illusion of doing any "work".
The system six is a six gallon plastic aquarium. Out of the box it contains almost everything you need for a minimal setup. It has a pretty small foot print and so it is very easy to find a place to put it. The filter is built into the hood. The filter is minimal but it easy to maintain. Every so often you have to replace the filter pad with a new one. There is also a bio wheel, which you can probably do away with. I left mine in.
A filter needs to do three things. Mechanical filtration removes particles. The filter pad does this. Chemical filtration removes stuff dissolved in the water. The filter pad contains a small amount of active carbon which does the chemical filter thing.
The bio wheel accomplishes the biological filtration. The bio wheel simply spins around in the outflow much like a paddle wheel. Bacteria set up shop in the wheel, and they turn ammonia (toxic to fish) into nitrite and then nitrate. Nitrate is mostly harmless, but at high levels it is not good. This is why you have to do water changes.
For a simple fresh water setup, the filter is adequate. Barely. I would have designed it to have a more powerful water pump, but as it is out of the box it works.
There is also a built in light. The light is very weak. Only 8 watts. This is another weakness with the design. Now some people have modified the hood so it has more light. You can upgrade it to have one or two 14 watt power compact bulb(s). This would give the little tank a lot more light, but if all you want to keep are a few fish then you do not need light. It would also increase the cost of the system. To keep it simple, and bring set up in an office, I decided to not modify it. I stuck with the stock lighting.
I did buy a different bulb. The aquarium came with a warm white (yellowish) bulb. I replaced that with a 14,000 k light - which looks more purple. I think these lights are better for plants.
In addition to the aquarium kit, I also got a fully submersible 50 watt heater with a built in thermostat. VERY IMPORTANT! A heater is required. Tropical fish like warm water. The office would get very cold when it was empty, and warmer when people were there. The heater would hold the water at 78 - 80 degrees no matter what. So you need a heater. If the temperature in the room is fairly constant a 25 watt heater would work, get the 50 watt.
After that you need a simple thermometer. Set the heater for 75 - 80 degrees (I set it to 80) and verify that temperature with a thermometer.
Now you are pretty much done with the hardware. It seems like a lot, but it really is not.
I wanted to keep live plants. The reason is because they look better than fake plants, the fish are in a more natural environment, they can add oxygen to the water, and they can remove nitrogen compounds - reducing the need for so many water changes.
But plants are also another problem. You have to keep them alive. They need light - which the aquarium out of the box does not have a lot of. So I had to select plants that would do OK in low light. I went with the Java Fern (seems to do great in low light) and some other plant that had wide leaves. Wide leaves = gathers more light = should do better in low light conditions. In theory. It worked for me.
But light I said, plants require nutrients. Now in aquariums of the past I had mixed results with plants. For the most part I was replacing them from time to time. I know why. The first aquarium I had I got when I was in 4th grade. And of course, it came with cheap gravel. The 55 gallon tank arrived when I was in 7th or 8th grade and used sand I salvaged from a pool filter. The substrate had nothing in it for the plants.
So for the little aquarium, I decided to go premium. I got a bag of this stuff. Seachem Flourite Red. It comes in other colors too, but the local fish store had red so that is what I got. This gravel is formulated for planted aquariums. It is pretty much natural fracured clay, treated in such a way as to lock the minerals in the clay. Plant roots can get what they need, but the gravel does not allow stuff to leach into the water. So now the plants can get the iron and other things they need - but the water remains clear.
But at $16 a bag, in a large aquarium it would get costly fast. However all I needed for the little tank was one bag. So that is not too bad. In fact, I did not even use all the bag. I have about 1/4 of a bag left.
I did not know if it would work, but I gave it a shot. The investment was not that much. In the old days, before things like this were available, to keep plants you had to go through a lot more. You had to have layers of subsreate. You needed medium size gravel, top soil, peat moss, and all kinds of crap. Pretty much you had to recreate a lake or river bottom. Not anymore!
WASH THIS STUFF OUT WELL. It is very dusty. Wash it until the rince water runs clear.
I also use another prodict for the plants. Seachem Excel. Plants need CO2. Now you can add CO2 to the water - but you need a CO2 tank and a pressure regulator and all sorts of stuff. Seachem Excel is a liquid that contains carbon compounds that plants can use instead of CO2. One large bottle of that stuff lasts forever as you only need a capfull per week. If that. I have gone for months without adding any and the plants did not die.
I do not add anything else for the plants.
Well that is pretty much it! One Marineland Ecliple System 6 aquarium, a 50 watt heater, a thermometer, and if you want plants the Seachem gravel and another 8 watt plant light bulb.
From there on, just go slow. I filled the aquarium with distilled water. Then I added buffer to stabilize PH where I wanted it. Again, the cost was minumal for this. The supermarket has gallon jugs of distilled water for about a buck each. Small aqaurium mens lower cost to fill.
This is not the time to add fish!!! You do not have a biological filter yet. This takes time to establish.
What you want to do now is put in the gravel (washed) and bio wheel. Carefully fill it with water. Set your heater to the desired temperature and plug everything in. Do not put in the filter pad. Not yet. Just use the bio wheel.
You will need some test kits now. At the least you need to get an ammonia, nitrite, and nitrate test kit. Then you need to cycle the aquarium.
To do this you need to introduce ammonia to the water. Ammonia is very toxic to fish. But fish produce ammonia as a waste product. You need bacteria to remove this stuff and turn it into less harmful nitrite, and then more bacteria to turn nitrite into nitrate. Your plants then use the nitrate. Balance everything and water changes do not have to be frequent.
So here is how I do it without using any fish. At first the water will have 0 ammonia. To produce ammonia all you need to do is add a pinch of fish food. It will break down to produce ammonia. You can also add a few drops of non sudsy ammonia directly to the water. You do not need a lot, just enough to start to turn your ammonia test kit green.
Then wait. The bacteria will find its way into the tank. Test ammonia every day, or every other day. Whatever you like. You will notice that ammonia levels will remain stable, then suddenly drop. Once ammonia drops to 0 then you know that the bacteria have arrived.
Next test for nitrite. If there is any, you are not done yet. Wait some more. After some more time you will notice nitrite drop, and nitrate rise.
DO NOT CHANGE WATER DURING THIS TIME. It will only take longer to cycle the tank.
Once ammonia and nitrite tests 0, do a partial water change to get the nitrate down to 20 ppm or less. Less is better.
Now you can add the plants. You can also put the filter pad in now. You do not put the filter pad in during the cycle because the filter pad will have a lot of bacteria in it. So once you remove that filter pad and throw it out - a chunk of your bio filter is gone. But if you cycle without any filter pad in place then you do not have to worry about throwing out pads later. The bacteria will be in the gravel and bio wheeel.
If you have a friend with an aquarium you can get one of their old filter pads. Put the pad in some aquarium water and swish it around. Scrub it lightly with a brush. Once a good portion of the gook on the filter pad is in the aquarium water, throw the pad out. This will speed up the cycle by adding established bacteria.
From here on go slow. You have a bio filter, but it is not strong. So add fish slowly. Figure out what fish you want to add - fish approiate for a 6 gallon tank. Do not go out and buy all the fish at once. Doing so could overload the bio filter. Start with one or two fish, wait a week, get one or two more, and so on. This gives the bio filter time to catch up to the bio load.
Do not overstock. The general rule for freshwater is one inch of fish per gallon of water. So in a 6 gallon tank that means you can keep one 6 inch fish, two three inch fish, 6 one inch fish, and so on. Overstocking is a killer, and a common mistake.
Test weekly for nitrate. When the test kit turns red, you probably need to change two gallons. Orange means one gallon. Yellow or orange-yellow means you are OK. You can keep nitrate at 0 with more bacteria. But these bacteria only live in oxygen free water. This is hard to do in a small aquarium. You need a deep gravel bed, or a lot of porus rocks, or something like that. These bacteria turn nitrate into nitrogen gas which then bubbles out.
In a small tank, nitrate is best controlled with plants and/or frequent partial water changes. How frequent? That depends on many factors. But the higher the bio load the more frequent the water changes have to be. This is why you need to test nitrate at least weekly. The good news here is that in a 6 gallon tank, one gallon is usually all you need to change. One gallon represents 20% of the volume. Or close to it. Changing one gallon is easy, takes only a little time, and you can keep using that distilled water and PH buffer for a low cost.
Balance the aquarium well, with fish and plants, and you can probably get by wuth 1/2 gallon changes. But I just do gallon changes.
And that is pretty much it. This all seems like a lot, but like I said it is really not. You just need some basic equipment, and a little time.
If you do not want the Eclipse you can get a standard squarium. But then you need to get the hood with a light, an external box filter, and all the other stuff. Cost will be about the same as the Exclipse 6, but you can probably get a slightly larger tank. Like 10 gallons at least.
The one thing I do not like about the Eclipse, other than the other limitations (weak light, could use a more powerful filter motor) is the cost of the filter pads. $10 for a three pack. I may try to see what happens if I rip a pad apart, dump the used carbon out, add fresh new carbon, and then lay in more floss. Should work fine and would prevent from having to buy more pads. It would be cheaper. But for now it makes it easy to change the mechanical and chemical media.
NEVER attempt to clean the bio wheel. Leave that thing alone. The gunkier it looks the better it works.
There are other all in one systems. When I got the Eclipse I did not really look at them too much. but had I looked, then I would have probably got the Bio-Cube 8 gallon tank. More light, more powerful water pump, and more options for the filter area. Also more money - about twice as much for the tank. And then you still need a heater and all the other stuff. But oh well. I did not. And for the way I have it set up, the Eclipse 6 is working fine. I am in no great hurry to change out the Eclipse.