Harlequin death

[Hercules99]

So today I've come home, looked at my tank and found one of my harlequin rasboras floating at the top.

For the past few days his dark patch on his sides have been faded but I didn't think it was any cause for concern. He's been keeping up with the others and eating normally up until now.

When I found him floating, hip fins were missing the tips and an eye was missing. Is it likely the other fish might have nipped at him after he passed?

The tank parameters are all within a safe margin
pH - 7
Nitrate - 0
Nitrite - 0
General hardness - 180

Their last water change was five days ago (28/10/19) and this was from the same water source all their changes have been from, they've never reacted badly before. I feed them twice a day with one fast day a week just before their water change.

The one that died was the smallest fish in the tank. I've never seen my betta try to attack them nor have they tried to attack the betta and I've only witnessed them glass surfing when they were new to the tank and during a larger water change.

What could have killed him? I'm quite new to the hobby but to the best of my knowledge I haven't done anything that should have a detrimental effect on the fish.

 

[melosu58]

I would be interested in what the ammonia and nitrites are.

 

[Hercules99]

I would be interested in what the ammonia and nitrites are.

The nitrite levels are 0, I have ordered an ammonia testing kit but it hasn't yet arrived. That said I did a water change as soon as I removed the dead fish so readings won't reflect the levels at time of death.

All the other fish are fine so far so I'm not sure if ammonia is to blame. The harlequin that died was always more faded in colour than the others and was my smallest male. I want to believe he was simply weaker (wishful thinking I suppose)