Is the fish being housed in a fish tank or bowl?
How many galllons/litres of water does the fish's tank/bowl hold?
How long has the tank/bowl been up and running with fish in it?
How many fish are in the tank/bowl?
Have you done anything recently to the water such as a water change or added anything new/different?
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You mentioned that "I just cleaned and changed the water a week a go".
Was all the water changed or only some of it? If only some of the water--how much?
Thank you for the information.
When you changed all of the water you effectively made the tank a new tank and as a result the tank water has started to cycle.
The fish's lethargy and bottom dwelling is being caused by the presence of ammonia in the water. Ammonia is harmful and lethal to fish as is a normal occurance in a newly set-up tank or a tank that has undergone a large or complete water change such as your tank. Ammonia is caused by fish waste and decaying matter and in an established tank will be broken down very quickly but in a new tank it won't.
Listed below are 3 links that will explain cycling, I suggest you thoroughly read them and follow my recommendations below.
In order to get through this most difficult period in the life of a new aquarium and save the fish certain steps should be taken to minimize the impact. They are:
1) Drastically cut down on the amount of food being fed as the excess fish waste produced by overfeeding is fuel for ammonia and nitrite growth. Feed the fish a pinch of food once every other day.
2) During the cycling process do not change or clean the filter nor the filter media as this is where the beneficial bacteria will grow.
3) Do not add any fish to the tank during the cycling process, even if one dies. The only time you would add a fish is if all the current inhabitants die.
4) I know it's a temptation but it would be best to not administer any products that eliminate ammonia and nitrites as these products are only a temporary fix and will delay the cycling process.
5) Test the water every 3-4 days and when either ammonia and/or nitrites begin to rise immediately do a 20% partial water change. Water samples can be brought to your local pet store for testing or you can test on your own using a standard test kit(s).
6) Add some aquarium salt to the water at a ratio of 1 tablespoon per every 5 gallons of water. When doing a partial water change add only the corresponding amount of salt to the water being added. The aquarium salt will help fthe fish cope with the nitrites.
7) Keep the water temperature in a range of 62f-72f degrees as this is the preferred range for goldfish. Also , water holds more oxygen at lower temperatures.
8) (You didn's speak of ph but just to make sure)--Do not attempt to adjust the ph at this time as changing the ph will further complicate matters.
Please note that in the future, it's best to never change all of the water. Although it seems like a good idea, changing 100% of the water, it causes problems in a fish tank.
Weekly 25% partial water changes are sufficient.
Best wishes and please let me know if you have any questions and please do try and read the links listed below.
http://www.thetropicaltank.co.uk/cycling.htm
http://www.bestfish.com/breakin.html
http://www.aquahobby.com/articles/e_syndrome.php
You make an interesting point about not having problems in the past.
In answer to your question about the water conditioner--this would absolutely have no effect as the function of water conditioners is to remove chlorine and chloramines from tap water. Ammonia and its follower nitrites will form regardless.
In my experience I have encountered a few fishkeepers who've noted that they didn't have any fish deaths or problems related to cycling in their new tank set-up.
Some possible reasons for this are 1) extremely healthy and tolerant fish
2) Large water to fish ratio meaning there's a lot more water per fish.
3) Fed the fish very little which would include feeding the fish every 3-4 days instead of every day.
4) Luck.
Another thing that could have an effect. You didn't mention if in the past you also changed the filter media with the 100% water changes. If you didn't it would've helped as beneficial bacteria colonizes on filter media.
Also--if you know someone that has an established fish tank, see if you could "borrow" some water, as much as possible as this water would help speed up the cycling process in your tank. Another established tank's old filter media would also be a benefit.
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