Guys, I know this is a frustratingly common problem, but remember, the majority of the bad info newbies get is from dishonest fish stores. in a way, they are victims too, albeit not as much so as the poor fish
More to the point, if a beginner leaves this forum due to rude comments, but then proceeds to keep fish without getting the proper advice, does this really serve the purpose of this forum?
Anyway, a 5 gallon (properly cycled, filtered, with heater) is the absolute minimum I would recommend to keep a single betta, but trust me, you and the fish would have far less headaches if you sprung for at least a 10 gal.
Regarding keeping "a few small fish" in unfiltered fishbowls (very rarely are these availible over 1 gallon), I think an illustration is in order here.
Imagine putting a family of four in a 6.5'x6.5'x6.5' (2x2x2Meter) room with a small 6x6" (15x15cm) grate in the ceiling for ventilation
(no fan), and giving them regular meals.
Any uneaten food and all waste goes into a hole in the floor.
No access to any hygiene or supplemental exercise equipment is given.
How long before the stench from the hole becomes unbearable?
In a couple of days, how much money would the parents be offering to get them all out of the room?
In such crowded conditions, how long before physical fights break out?
How long before disease breaks out from the unsanitary conditions?
In a few weeks, how much bone and muscle loss will have occurred due to lack of exercise?
Of course, even this fails to illustrate how bad bowls are on several points.
To make it closer to what the fish are experiencing, we have to make the family in the above example unable to breathe air, instead having to breathe water...
That's right, we fill the room with water.
Now
everything that was in the hole is dissolved throughout the room, the family members are in constant contact with it, and BREATHING it, 24/7.
In addition to the obvious ways this makes things exponentially worse, there is the factor of ammonia and nitrite.
Uneaten food and fish manure gives off ammonia as it breaks down, and the fish themselves give off ammonia in their urine and through their gills at a fairly constant rate.
It is very difficult to overstate how toxic ammonia is to fish, I believe most beginner, many intermediate and even a few advanced aquarists underestimate just how deadly it is.
Here is a link to an article explaining the toxicity of ammonia.
Note: For conversion purposes mg/l (milligrams per liter) is the same as ppm (parts per million)
https/edis.ifas.ufl.edu/fa031
Unionized ammonia (UIA) is in particular ridiculously toxic, as indicated by this quote from the above link:
""Anytime the UIA is higher than 0.05 mg/L, the fish are being damaged.""
To put this in perspective, there are about 20 drops in a milliliter so this is the equivalent of
ONE DROP of UIA in a 1000 liter (about 265 gallon) tank!
This is below the level of detection for many test kits, most of which do not give separate readings for ionized and unionized ammonia, instead giving one number for total ammonia.
In the nitrogen cycle, both ionized and unionized ammonia are broken down by the good bacteria in a filter to nitrite, which unfortunately is only slightly less toxic than ammonia, being harmful at levels as low as .10ppm (1 drop per 133 gallon)
http/vri.cz/docs/vetmed/50-11-461.pdf
IMO, to summarize the way it blocks oxygen uptake by red blood cells, nitrite can be called the "carbon monoxide" of aquariums.
In the course of the nitogen cycle, nitrites eventually break down to nitrates, which are
much less toxic to fish, considered safe at levels below 250ppm (about 2 teaspoons in 10 gallons) THIS is the ONLY waste that weekly water changes can keep up with.
The nitrogen cycle WILL NOT HAPPEN fast enough to be of any help to the fish until the aquarium has been properly cycled.
For more on cycling, Please visit:
http/www.fishforums.net/index.php?/topic/421488-cycling-your-new-fresh-water-tank-read-this-first/