Fish Dying One By One

[cms091]

I lost another fish on sunday. It was a tiny three-line cory that hadn't grown since I bought it about 6 months ago. It just lay on its side and couldn't swim, so I euthanised it.
 
I've got two tanks, Aqua One 980 (215l) and a juwel 180l. Both tanks were established over 3 years ago. All the fish are in the 215l at the moment as I had a cyanobacteria outbreak before christmas and decided to dry it out, get a new filter (tetratec to replace the in-built one) and re-do completely. So I'm waiting for a warm spell to wash the sand! 
 
So I've got 10 three line cories, 1 san juan cory (can't find any more!), 3 dwarf neon rainbows (waiting to get more) , 12 zebra danios (which really belong in the cooler 180l), 2 siamese algae eaters and some assassin snails. So I think I'm way understocked.
 
My problem is, I lose ONE fish and wait a couple of weeks, which sometimes stretches to a couple of months, and start thinking it's time to re-stock and another one dies.
 
I've never has a problem with water quality, apart from the tap water being very hard and 50ppm or over nitrate, I'm always 0 ammonia, 0 nitrite.
 
Does this happen to other people? No dramatic mass deaths, nothing to see on the ill fish, just dying one by one over the months and years. Should I just say - that fish never thrived, it was bound to die sooner rather than later? Except I used to have 3 SAE and one went the same way about 2 years ago. Seemed fine one day, then just lay down and died.
 
Any clues?
 
Or should I re-stock sooner!
 
Cathy
 

 

[phoenixgsd]

did you move all your media over when you changed filters? what are your current water stats now? how often and how much do you water change?

 

[cms091]

I moved the 12 zebra before christmas, into a well establish tank and monitored the levels afterwards.
 
0 ammonia, 0 nitrite. 25C. 
 
I don't test for nitrate as it is always high due to tap water level being 50+. I keep it as low as I can with plants.
 
I didn't move any media as I wanted to minimise the chance of the cyanobacteria coming across too.
 
I have lost this one tiny cory since christmas. I really think moving the fish is a red herring. I have always lost fish in this way, over the past 10 years.
 
Cathy

 

[spongy]

Not just old age is it?

 

[Sammy1911]

I find the same with my tanks tbh - my water is great, i do weekly water changes without fail and have it heavily planted i dont overfeed but i typically have losses every couple of months. im currently planning restocking/topping up so i have got the qt running and my main must know my intention coz ive lost two fish in the last week (of my existing stock), no change to water stats and no signs of sickness or anything... go figure!

 

[cms091]

Not just old age is it?

No. My 3 SAE were bought at the same time as inch long babies. All three got to adult size. One died other two have lived another 2 years!
The latest loss, the little cory, did have something wrong with it.
 
I think the trouble is, with little fish especially, that because there are no preditors, the ones that shouldn't survive to adulthood get to be that little bit older then the defect kills them off.
 
Cathy