a. There is excess food all across the gravel, shall I swirl the water around and take a picture so you can see it all floating up?
b. The test was taken before the fish were put in, not after.
c. There were cherry barbs in it, as said above.
d. The nitrate in the big tank is 23ppm.
e. pH in big tank is 0.0
And I don't know if my test kits are right.. I use this
test kit, is that an accurate one or do you know?
I don't know what the problem is, I already found out why they died.
a. Remove all the excess food imediatly, you should have done that as soon as you got back, ammonia is always more concentrated at the bottom of the tank which is partly why so many bottom dwelling fish are so sensitive to even the smallest fluctuations in ammonia, the rotting food would also have made the ideal conditions for growing deseases like columnaris, fish TB, fish fungus and internal bacteria.
b. You should have tested the water stats after the fish were put in and not before as this is when the tank is most likely to experience water stat fluctions, after the tank bioload had increased- can you give us some recent stats?
c. Even if the tank was cycled, thats alot of fish to just add in all at once and could hav eeasily caused the tank to mini cycle.
d. fine nitrate readings there.
e. Its near imposible to have a PH that low, those results simply cannot be correct. Since you don't realy know wether the PH fluctuated in the tank its difficult to rule out wether PH shock also contributed towards the fish's deaths.
Apart from getting new test kits and making sure you are using them correctly, keep doing those water changes with dechlorinator on a very regular basis and watch you fish's behavior and appearance closely in every aspect to make sure there are no deseases growing in the tank unoticed.
Its hard to say what happened here- although most likely a number of events that contributed to the fish's deaths i.e overfeeding, adding large numbers of fish at once to a tank and water quality issues, but now what we need to do is to help prevent the same thing happening again.