yes, in order to keep your fish alive, it's best to clean the fish bowl as often as you can.
It is best that all fish have a filter besides Betta fish. Betta fish don't need filters cause the filter pushes them over with their big fins. Goldfish should have a filter on there tank because they are often overfed. If you have a filter you won't have to change the water as often. The only fish that shouldn't have a filer in captivity are Betta fish.
they eat fish and drink water to survive
They need oxygen definitely to survive. They get this from filtration through their gills. As far as light is concerned, they do not need light to survive as many live below the layer in the ocean that light can permeate. There are fish that lice in total darkness. They have adapted over the years to exist in these conditions.
Water is important to fish because it provides oxygen for their respiration, helps regulate their body temperature, and serves as a medium for waste removal and nutrient absorption. Water also supports their buoyancy and allows them to move and hunt for food.
From what I understand it is at least 2 gallons of water per inch of fish. More water is always better than less. Remember fish need room to move around and swim. The typical fishbowl one might buy from the store is not sufficient for most fish and as an aside, the shape of those types of bowls negatively affects the fish's respiration. Best to get a regular shaped tank (square, rectangle, etc.) and use more than enough water.
one time a month
They won't react at all, because fish need to be placed in room temperture water every time you change their water.
It sounds like your fish has fungus over its eyes and skin. That indicates terrible water conditions. All fish need to have clean water. Change the water! Successfull fish keepers change at least a part of a tanks water weekly.
If you don't have an aerator, you need to change the water very other day at least--but take care not to stress the fish in doing this. The easiest solution is to get a proper aerator.
It could well be the fishes natural coloring. Or you need to change the water ASAP. If you don't get ready for your fish to die.
yes but it would need a heater as they are both tropical fish and you would need to change the water alot.
When its dirty you need to change the filter.
Saltwater fish require salt water, and fresh water fish need fresh water, you can't mix them, or the fish will die. You need to look at each individual fishes needs as to what temp they need their water to be. There are some saltwater fish that can survive in fresh water, but it is not healthy for them.
Depends on the fish.
It probably means that you urgently need to do a water change. ASAP. Fish gasp (breath harder) when the oxygen level in their water gets low.
As soon as nitrates have reached zero. Don't ever change more than 20% water a week. If you have fish in the tank during the cycling process you will need to change some water if the nitrates are in the deadly range to keep your fish alive. Otherwise I recommend an additive such as Prime to keep nitrates from killing fish during cycling.
All fish need at least a 50% water change weekly. Good practice is to change 10% daily and 50% weekly. It is assumed that the tank is large enough for the fish (1 inch of fish needs a minimum of 1 gallon of water) and filtered properly too.