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About 2 months ago I restocked my 60 liter tank. It was cycled years ago but old age took it's toll and I was left with a single tetra and a thriving shrimp population (Something from the caridina family but in pure wild colouration).

I went to a local shop and bought a group of 10 Boraras brigittae/mosquito rasbora. 2 of which died within 24 hours but the rest is doing well. I also bought a group of 5 small black and white aspidoras, not entirely sure of the species most likely Aspidoras pauciradiatus. These did fine up until 2 weeks ago when three died in as much days.

I'm a bit baffled by that, I got temp constant at 25 degrees C, my water values are as steady as they always are (if not my shrimp would be the first to notice). I change 10 liters weekly. I've kept aquaria for about 15 years now and never lost fish due to unknown causes (Excluding transport shock). I'm tempted to run out and restock but this would be pointless if there's something wrong in the tank.

Anyone any ideas? Pointers?

While your tank was cycled; it was only cycled enough to handle the load of a single tetra and the shrimp. Its very possible when you restocked your tank it cycled again as the bio load you put on it was significantly more than what it was currently handling. I'd do a ammonia, nitrite, nitrate check on the tank. You really needed to do this test when you started having problems to help narrow down what the problem might or might not be. I'd still get it tested and see where its at before adding fish. I'd up your water change volume to 20-30 liters.

That's my best guess as to what went on but there are always other possibilities.

I did test, both before restocking, straight after and again 3 weeks later. Either my test kit is due for replacement or there were no fluctuations. Besides, if it was anything chemical I would have expected casualties straight away, not a few weeks later.

You could try adding a filter maturation liquid. (I never use these, but a lot of other people do.) If you bought again you would need to re-stock gradually - 5 or 6 of the Boraras - and feed sparingly for the next week or so.

I don't think it is an ammonia or nitrite problem. You wouldn't have any shrimps left by now it that were the problem.

Hi Wijnands

not entirely sure of the species most likely Aspidoras pauciradiatus. These did fine up until 2 weeks ago when three died in as much days

&

I got temp constant at 25 degrees C,

A couple of things here.
The temperature may be to high for the Aspidoras. I find that tend to be more at home in temperatures between 21 & 23 degrees C. Unless the water has a high level of dissolved oxygen.
Also:-
Did you find the bodies of the Aspidoras or just found that when you counted them, there were 3 unaccounted for?
Reason being is that nearly all (if not all) Aspidoras species tend to vacate the aquarium unless it has a tight fitting cover glass.
Believe me, they seem to be able to find and get through the smallest gap

I could try lowering the temp I suppose although the remaining to are happy and have now almost reached adult size. The water is quite well oxygenated, I've got a little bit of tubing on my filter exhaust that draws in air to make a stream of tiny bubbles. I did check http://www.planetcatfish.com/catelog/sp ... ies_id=383 before purchase so I'd expected 25 degrees to be acceptable.

These three did not evacuate, I found bodies, or remains of them anyways, anything dead in my tank immediately attracts all the shrimp and snails.

I'm still not entirely sure what to do, the remaining two seem to do fine but they did seem happier in a large group. I do wonder if they'd do a mixed school with any of the smaller corydoras species?