Fish Problem.

[lavyheed]

My 4 foot communal tank which has been well cycled has a major problem! I have Columbian tetras pencil fish a few harlequins and a couple of cory's and a dwarf gourami.  I had 4 columbians and out of the 4 I have two left, but one is showing signs tonight. I've lost 3 out of 6 pencils and way back in the begining it started with the guppies  and out of 5 there is one left
 
Everything was fine until the last couple of days the fish have been dying! They all show the same symptoms which is like they are swimming with their head and going round in circles. This only lasts for a day and then they are dead in the morning. These fish have been in the tank a while and the water ph is fine and all the nitrates ect are fine and so it the temp.
 
When it first started happening I did a water change and it's still happening. The filtration is a fluval 403.
 
Anybody have any suggestions?

 

[Baccus]

 Ok there are quite a few questions we will have that need answering so hopefully we can help you and your fish. We will need to know how long your tank was cycled and how. Did you test the water yourself or did you get the pet/ fish shop to test the water. Do you know the actual results? Many shops say " all fine" when it really isn't. If testing yourself did you use paper strip tests which are pretty well known for being inaccurate or did you use liquid tests?
Have you by chance tested the water coming out of your tap? Some places naturally have high nitrate levels in the water supply.
Have you added anything new to the tank? Live Plants? A new fish? Even an ornament that perhaps was not fully rinsed before being added to the tank?

 

[CoryLover95]

As Baccus said, in order to help you better we need to know more.  I'd suggest filling out this template (from the Please Read This Before Posting to Emergency Section thread pinned at the top of the Emergency section).
 
 
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Tank size:
pH:
ammonia:
nitrite:
nitrate:
kH:
gH:
tank temp:

Fish Symptoms (include full description including lesion, color, location, fish behavior):

Volume and Frequency of water changes:

Chemical Additives or Media in your tank:

Tank inhabitants:

Recent additions to your tank (living or decoration):

Exposure to chemicals:

Digital photo (include if possible):