You need to aerate it. If you have no filtration/aeration system, get a cup, scoop up water and drop it back into the aquarium from a height of about twenty centimetres. Do this for one minute every four or five hours until you can set up a filtration or aeration system. Overstocked tanks (too many fish) will use up oxygen faster than it can be replaced, even by an aeration system. Adding live plants will also help to remove carbon dioxide and add oxygen to the water.
If a goldfish frequently comes up to the service than this is an indicator that the dissolved oxygen levels are too low and the fish is therefore sufficating. To fix this do a large 50-75% water change and install an aerator in the aquarium.
No, plants in an aquarium provide oxygen to the animals.
It depends on what kind of fish, and the size of the aquarium.
Team Umizoomi - 2010 The Aquarium Fix It 1-2 is rated/received certificates of: Australia:G
merchanical source of oxygen
You can control the oxygen through aeration
A Balanced Aquarium is one wherein the Oxygen/Nitrogen cycle is self sustaining.
Yes, aerator and plants are important in the aquarium to add oxygen in the water for the animals there in.
The some need of the animals in the aquarium that plants can provide is oxygen.
Oxygen
Depends on what kind of fish they are, but it sounds like they are not getting enough oxygen, and/or the water temp might be too low.
for the plants which make some of oxygen