That depends on the number and size of the fish you have added in the tank. But as blanket recommendation you can do 50 percent water change once in a week.
It's recommended to perform a partial water change of about 25% every 2-4 weeks in a 29-gallon fish tank. Additionally, you should clean the filter once a month and regularly remove any debris or waste from the tank to maintain water quality and a healthy environment for your fish.
That's perfectly normal for a betta.
you should change it every week so it will always be clean.
The charcoal filter in a fish tank should be changed every 2-4 weeks to maintain water quality and keep the tank clean for the fish.
The rule of thumb is usually a gallon per fish, so six gallons would be good. If the fish are on the large side (like a goldfish), then a seven gallon tank would be ideal.
The fish are not bad together. But way to many fish for a ten gallon tank. You put one fish for every gallon. They will probly do fine but you will have to clean more.
A betta fish would be much more suited to a 1 gallon tank than a 'variety'. You shouldn't keep much more than one fish per gallon anyway.
Depends on the kind and size of the fish. You should also take in to consideration how large they will get at adulthood. A good rule of thumb to go by is 1 gallon of water for every 1 inch of fish. So for example: 3 2" fish should be in at least 6 gallons of water. To be safe I would put them in a 10 gallon aquarium.
Betta fish are about the only kind of fish that can survive with no filter. They prefer still water or a very gentle current, so as long as you are keeping their water warm and clean (at least 80* F) they will thrive in a one gallon, unfiltered bowl. Change the water at least weekly to keep a one-gallon betta tank clean. Change more often in anything smaller (and it's not recommended to keep them in anything smaller).
I personally would empty it, then scrub it clean and use it occasionally as a flower vase. It is not large enough to keep any kind of fish in properly. The basic rules for keeping fish successfully are. :- 1 inch of fish needs at least 1 gallon of water (a Betta is a 3 inch fish). Every tank must have a permanently running 'cycled' filter. Every tank must have at least 50% of its water replaced every week. The above is not completely true. A Betta in a half gallon tank should have half of its water replaced each week. You should use a conditioner with that water (mine came with Nutrafin Betta Bowl Water Conditioner). I also make 20% of it HBH Betta H2O, which can be bought in bottles.
Once a week
Yes, since Guppies and Neon Tetras are small fish (and stay small), there should be no problem with them living comfortably in a 2 gallon tank. You should add a little filter and air bubble combo to keep the water clean and aerated. Since these are tropical fish, you should also add a small heater and a thermometer. Goldfish do not need a heater but tropical fish do.