Tetra's Are Fading Away

[ShinySideUp]

I have Black Phantom Tetra's and Diamond Tetra's and there lives are, one by one, slowly sinking in the West. They are between two and five years old and I might think they are eaching the end of their lifespan but I am a little concerned there might be a problem with them as I have lost two or three in the last couple of weeks. I have six foot tank, heavily planted over 2/3 of the tank. Stats are perfect, really, spot on.
 
What is my problem? Old age, food issues? The fish have died or have been euthanased but their symptoms are not similar. Sometimes they fail to swim properly, others have an odd shape, another seemed confused.
 
My personal opinion is that they are just reaching the end of life but it's a little distressing nevertheless.

 

[looking-glass]

have you tested your water it could be old age as you say though youve done well to keep them for that long it shows they have been well looked after

 

[BerryAttack]

if you are adding in new fish to the tank then they can be bring things in that are affecting the older fish. or it can be aggression from other fish and if they don't have proper schooling numbers then the aggression in the group.
 
if you added any new plants in then there could have been chemicals that are affecting them.. so give them a good rinse and soak a night before adding them in.. just learned that the hard way with my shrimp.. bummer
 
if you think its the food, change it up.. cut feeding for 3 days to allow everything to clean out.. then feed every 3 days, once a day (enough to eat in a min or two) and do a large water change.. treat the water and check the stats. 

 

[ShinySideUp]

Nothing new has been added to the tank for months apart from fresh water. My water is fine and the food is a large assortment of flakes, bloodworm, brine shrimp, algae tabs and algae flakes plus others. I'm pretty sure it's old age as really it can be nothing else. I suppose I'm just thinking out loud in case I've missed anything.