Swordtail ill or just dealing with the cycle

Question
Okay, we have set up a 20 gallon take and we did it all wrong.  But we have stayed diligent with it and now we have that tank under control and only lost one fish.

We have set up a 55 gallon.  It is now going thru the cycle.  The tank is going on the second week of being set up.  It is cloudy (bacterial bloom) and the ammonia, as of today, is at .50.  Now I know that the ammonia will spike and then it will go back down when the nitrites go up, etc, etc.  pH is 7.6/7.8 - no nitrites at this time.  Again, we just set this tank up and we are in our 2nd week and we have done two 20% - 25% water changes (we have very high pH in our tap water so we have to do water changes with bottled spring water to get the pH down).

We started the tank with 3 swordtails - we have lost one to pop eye and now we have one that is acting really strange and with all the research I am still not able to figure out the problem.....3rd one is doing fine and we have 3 blue platys, who also seem to be doing fine.

Now my swordtail - at times he will go to one end of the tank and just swim from about 1 - 2 in. from the top of the tank down to the gravel.  He will do this for quite sometime.  I have also noticed a single then hair like string from the bottom side of him.  It is hard to see and you really have to look at him to see it.  He dorsal fine lays completely flat.  He gets very, very still and stays on the bottom - still to the point that his fins are not moving.  He hides allot also........I keep waiting to come in and find him on the bottom on his side as the pop eye one was.

Is this just a reaction to the cycle or is there an illness concern?  

We have an under gravel filter and a 40 gallon waterfall (power) filter.

Answer
Hi Cherisa;

I think he's being poisoned by the ammonia. His dorsal fin being down and lethargic at times are major signs of it. The string coming from him could be a digestive issue related to stress or even an internal bacterial infection. Swimming up and down the sides can indicate that he's trying to escape the toxic water. He's basically looking for a way out to safer more comfortable water.

Make a 25% water change every day for the next 3 or 4 days and stop feeding the fish for that length of time. After the three or four days, you can feed again, but feed only two flakes of food per fish once a day. This is basic survival rationing, but it is safer for them to be a bit hungry than to die of ammonia poisoning. The 3 or 4 day "fast" may help his digestion improve too.

I hope he feels better soon...

At Your Service;
Chris Robbins