Diagnosis?

[dr hfuhruhurr]

Hi All,

Could you please use your experience to diagnose what is going on in my fish tank.

8 Swordtails (2 males, 6 females) were added last Sunday after the tank had been cycling fishless for 4 weeks. For the first 5 days they were lively and frisky but on Saturday morning they were slow and shoaling quite densely - staying at the bottom of the tank.

Apart from the slow swimming there does not appear to be any outward signs of illness, although I have noticed on some of the females that the lower part of the abdomen is either grey or nearer black.

The tank has undergone two water changes during the week
Wednesday: 15%
Saturday: Two Thirds

The Nitrate level was raised yesterday, but after the water change, it was minimal. I didnt feed them yesterday, but they came for flakes this morning and looked quite content during feeding time but returned to the bottom of the tank afterwards.

Which of these scenarios seems most likely.
1) The fish are overfed. I think I may have fed them twice on Friday by mistake
2) All the females are pregnant!!
3) All the fish are ill in some way.
4) The water in the tank is a bit unstable and the fish are sulking
5) Some or none of the above.

On the plus side, there have been no fatalities amongst them or the shrimps they share the tank with.

Any wisdom on the matter would put my mind at rest.

Thanks

 

[Glod]

How large is the tank ? What are the water stats ? (PH, Ammonia, Nitrite, Nitrate). 2/3 is a lot of water to change in one go, it would be preferable to do smaller changes a day or so apart. I definitely wouldn't change more than 30% at a time without a very good reason.
Were the fish acting sluggish before or after the water change on saturday ?