Fish Losing Fins & Odd Shapes

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Tank size: 42 US Gallons / 160 Litres
pH: 6.8
ammonia: 0
nitrite: 0
nitrate: 20
kH:?
gH:?
tank temp:26

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

I have a blood fin tetra who came with my 2nd hand tank. Seemed fine for first 2 weeks, now in the space of a couple of days it looks like his fins have rotted / been nipped away, and now his body looks very twisted (could be skinny?) and looks like he's been nipped all over the top & bottom of his body. See photos below. Possibly spreading to other fish - one swordtail / platy also looks to be a strange shape, so I've moved both of them to a quarantine tank. One other swordtail/platy was missing dorsal fin, tried to move him to but he escaped and is now hiding somewhere.

Tetra has seemed a bit unhappy for a couple of days before I noticed symptoms, other than that I've seen no behaviour condition changes with any of the fish.

Volume and Frequency of water changes: Only had tank 3 weeks now, was already cycled, did first major water change on the weekend - 30%.

Chemical Additives or Media in your tank: Just foam in the filter.

Tank inhabitants: 3 sailfin mollies, 10 swordtails / platys, 1 plec & 2 kuhli loaches

Recent additions to your tank (living or decoration): none

Exposure to chemicals: I added PH down & Prime (to remove the chlorine) to the water added to the tank.

Digital photo (include if possible):

Healthy blood fin tetra:



Now 3 weeks later:

 

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Update: blood fin tetra has been lying on his side on the bottom for a while now, still breathing but doesnt look good at all. I've removed him from the quarantine tank & put him in a small plastic tub - dont think he's going to last. Looks like his skin is flaking off all along the top & bottom of its body.

Managed to get the 2 dodgy looking swordtail/platys into the quarantine tank. One looks like he might be losing his dorsal fin slightly, the other looks like a really odd shape, almost like its lost weight, which has bent his overall shape. I observed both of these symptons in the tetra thats almost gone. I'm hoping to save these two - does anyone recognise these syptoms, and have any idea how I can treat?

 

[Colin_T]

The sick looking bloodfin appears to have a bacterial or protozoan infection. They can both be treated with a broad-spectrum medication like "Waterlife Protozin" or "Wardley's Promethyasul". Both of these problems will affect any fish in the tank and can cause the symptoms you describe, bent back, clamped fins, grey or cream coloured film over the body, etc.

I would also check the water quality in the tank, (ie: ammonia, nitrite & nitrate). If the tank was moved and the filter turned off for any length of time, it could have caused problems, (mini cycle) and this could have caused the fish to become weak and allow the bugs to affect them.

Before you start treatment, do a couple of big (50%) water changes and gravel clean the tank. Remove any carbon from the filter to prevent it absorbing the medication.

 

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The sick looking bloodfin appears to have a bacterial or protozoan infection. They can both be treated with a broad-spectrum medication like "Waterlife Protozin" or "Wardley's Promethyasul". Both of these problems will affect any fish in the tank and can cause the symptoms you describe, bent back, clamped fins, grey or cream coloured film over the body, etc.

I would also check the water quality in the tank, (ie: ammonia, nitrite & nitrate). If the tank was moved and the filter turned off for any length of time, it could have caused problems, (mini cycle) and this could have caused the fish to become weak and allow the bugs to affect them.

Before you start treatment, do a couple of big (50%) water changes and gravel clean the tank. Remove any carbon from the filter to prevent it absorbing the medication.

Tetra has now died Bent swordtail / platy is still looking very bent & sad, other one with small fin seems ok, not sure if he should be in the quarantine tank now...

I'll do the water changes, but the gravel should be clean (cleaned very thoroughly 3 weeks ago). When I got the setup the filter media was left out of the water for about an hour, but I did chem tests every day, and the ammonia was 0.15 for the first 2 days only, and nitrite 0.25 only for the first day, all zeros after that. The only chems I dont have test for as water hardness & chlorine, although I used some Prime to get rid of chlorine. Could it be one of those causing this?

I'll also checkout my lfs tomorrow for meds - I cant get to it until then

Thanks for your help!

 

[Colin_T]

Hardness and chlorine won't cause that sort of problem, nor will water conditioners.
The fish could have been weakened by the move and were more susceptible to developing an infection.

You should do a gravel clean every time you do a water change. This is especially important if you are going to treat the tank as it helps remove most of the gunk in the substrate. The gunk will harbour lots of good and bad bacteria and the less gunk and bacteria in the tank, the more effectively the medications work.

To work out the volume of water in the tank
measure Length x Width x Height in cm
divide by 1000
equals volume in litres

When measuring the height, measure from the top of the gravel to the top of the water level. If you have big rocks or driftwood in the tank, remove them before measuring the height.

 

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I've just had to move another swordtail / platy to the quarantine tank - his scales between his mouth & eyes look very loose (peeling off?), and have turned purple. Other small fish have been trying to nibble at them. He was starting to look miserable in one corner of the main tank.

I wonder if this will affect more in my main tank?

Shame as they all seemed very health for the first 2 weeks, right up until my first water change.