It doesn't necessarily have to follow the Walstad method 100%, a cycled filter and some fast growing pond weed could sustain a tank for months on end.
I can turn the If the "Walstad Method" is being used by that person, why wasn't that mentioned? argument on it's head and say, how do you know it wasn't filtered if it wasn't mentioned, it works both ways.
In my opinion, some people really do disguise opinion as fact, this isn't just relevant to what I have discussed, but quite a lot of the posts in this section are so biased, I've heard it mentioned many times before: that anything under 5 gallons is a death trap, wow, what a statement, there are hundreds that keep Betta's in smaller tanks than this that do fine, the thing is, you have to think outside of the box before presuming things, if a betta has survived without water changes for 8 months, then something must be working, if the tank didn't have a filter the betta would be dead by now, so it's obvious that it has a filter, as for nitrates, dangerous levels begin at about 400ppm for Betta splendens, after 8 months, levels would be quite a lot higher than this, so something must be reducing them, be it Plants, or anaerobic bacteria that colonize in the substrate.
I agree that Betta 898's post has no credibility, but what I'm trying to say is, that it is possible for a betta to live in a tank for 8 months without a water change, people blindly dismiss that without taking all of the options into hand.
100 agreed with above.
i used the walstad method for almost a YEAR. no waterchanges at all and all parameters 0. just weekly top offs. so it is worth considering this method. and very easy to set up.
however that is not the purpose of this thread. the only issue with a 1 gal is the heat. they do make very small heaters but even they are too big for a gal. a simple incandescent desk lamp would do just fine heating the water during the day with a temp drop at night when you turn it off. which is fine as fluctuations in water temp happen in nature-even in the daytime. its called a thermocline and they are found in any type of natural system.
if not using the walstad method for ammonia control either 50%water changes every day/other day without overfeeding should suffice. HOWEVER, building a DIY sponge filter with a very small container(such as a small fishfood pot or even an empty and clean prescription bottle) would work JUST fine. so-
to the OP-
if upgrading is NOT an option and you are serious about the welfare of the fish, stick a desklamp over the tank and monitor the temp with a stick on thermometer until you determine the correct distance to place the light to heat the water to about 76F. also, buy a small (and cheap) airpump to make your very own tiny filter. they work so much better than any of the small commercial filters and are absolutely customizable to take up the least amount of space. also limit the substrate.
too many times there is far too much criticism for people wanting help with small tanks. sometimes it is JUST NOT POSSIBLE to get a bigger tank and to be told you will kill the fish is simply absurd. lets try to find a solution instead of have to's and have not's.
if the OP or anyone else would like instructions on how to make your own sponge filter very easily and cheaply (i know there is an old thread out there that lots of folks link to, but it is actually more complicated than it needs to be) feel free to PM me. i have made dozens of them and have them in all my betta tanks which range from 2-6 gals. and no- none of my fish are suffering. all just as active and healthy as the next one.
just my two cents as i HATE to see people criticized for small tanks. they are not a death sentance for a betta! a litre, sure, but not a gal.
cheers