Killifish Is Floating At Surface D:

[ATK!!!]

Hello everyone, haven't been round here for quite a while but sadly something rather disturbing has happened. Around a year ago I bought a pair of Fundulopanchax gardneri (Pretty common Killifish) to add to my already mature planted tank. Sadly around 2 months ago the male died, seemingly of natural causes and after that everything seemed to be fine, however yesterday the female started to act very lethargic and would not eat any food. Today I woke up to her floating near the surface of the inlet for the tank, still breathing at a normal rate but not moving her fins at all and her spine seemed to be bent slightly. I hoped that she was just acting a little strangely but she has continued to do this for 7 hours and is now currently still floating, although she has changed position a few times so she is still capable of swimming.
 
Here are my tank parameters:
 
Tank size: 180l Juwel Rio 180
pH: 7.32 (Seneye measurement)
ammonia: 0.002 (Seneye measurement)
nitrite: 0 (Simple liquid test kit)
nitrate: Could test for this but it's not really easily done or needed
kH: Not known
gH: Also not known (I have very hard water in this area naturally though so..)
tank temp: 24.5C (Higher than usual due to heatwave, normally 22.5/23 ish)
 
Tank inhabitants:
18 Ember Tetra
6 Pepper Corys
6 Splashing Tetra (Largish size)
3 Nerite Snails
5 Amano Shrimp
1 Twig tailed Catfish
And of course the one ill Killifish
 
Here's a picture of her in her current condition:

 
If anyone could offer some advice that would be great, she's really not looking well. 
 
Also one thing that may be the factor is that they're supposed to live for around a year apparently and she is older than that now?! (This may be incorrect, I heard it from the seller). If you could tell me whether it is simply old age, even that would offer some consolidation.
 

 

[Chad]

I would say two years is average with 3 being long for a Gardner's killi it being a "non-annual" killi.
 
But I have read that temperature can affect lifespan with tropical temps shortening it. When I read your post my first thought was age.
 
If it was mature when you purchased it, which could have been 6 months old then you have had them for year...1.5 years old, maybe older.
 
While short of the 2-3 years it's not outside of the ordinary to consider it old enough to become weak and pass on.

 

[ATK!!!]

When they were first purchased they were already fully grown and coloured so I suspect you're right at the 1.5 years old mark now I think of it. Thanks for giving me the correct lifespan though, I'll bear that in mind. Would you say that these are natural symptoms for an ageing fish? None of my other fish have really died since I bought and prepared the tank a few years ago so I haven't seen any reaching the end of their lifespan :l
 
They really have been a lovely pair of fish so I may consider buying another pair in the future, I just hope that this fish isn't suffering too much at this point

 

[Chad]

Yes, I feel those are pretty natural symptoms. They pretty much get tired, don't swim as much, nothing seems to be wrong other than that and the other fish seem fine.