male Dwarf gourami

Question
hey i just lost a male dwarf gourami today and have no clue why it died and am concerned about the other dwarf gourami who is also in the tank with it. heres some detailed information. He was also wedged at the top of the tank in between the filter and glass near the top of the tank but not outside the water.
168 litre tank
been in operation for 3 months with current filter
396 gallon/hr canister filter
heavily planted tank
80w of 10000k lighting (6 hours a day)

fish present
2 oto cats (2 months)
4 clown loaches (2 weeks returned them 2 days ago; didn't want them as they were hiding all the time)
1 sae (1 week)
2 dwarf gourami (1 week)and 1 of them died

5 days ago before i returned the clown loaches i did some water tests
ammomium : 1.1
nitrate: 0
nitrite: 0
did a 45% water change

1 day later
water change 20%
ph: 7.6
ammomium : 0.25
nitrate: 0
nitrite: 0

2 days later
water change 10%
ph: 7.4
ammomium : 0.1
nitrate: 0
nitrite: 0

3days later
ph: 7.4
ammomium : 0
nitrate:
nitrite:

Answer
Hi David,
This is an unusual case.  Because the tank is 3 months old and you still dont have signs of Nitrates.  I would believe a tank should be cycled by then.  Nitrates should be present in all cycled and mature tanks and is not necessarily bad.  It shows you that your tank is cycled and the beneficial bacteria are doing its job.  Anyhow, by 3 months, the tank should be cycled and you shouldnt see signs of ammonia nor nitrites.  But you should have readings of nitrates.  The only possible reason that a tank doesnt have nitrates is if it was HEAVILY planted with a minimal amount of fish, therefore the plant soaks up all the nitrates to not show up in kit readings.  But if that was the case, the ammonia would be gone too.  By any chance are you using test strips to test?  Test strips are very inaccurate and may give false readings.  

However, if the tests are right, then 1.1ppm ammonia is fairly high.  During cycling, we try to keep ammonia and nitrite ppms below 0.50ppm to prevent intoxication.  I would think it was the ammonia that killed the gourami.  It was a smart thing to do the 45% water change on the day with the ammonia at 1.1ppm.  If your tank is not cycled yet, continue to do water changes to keep both ammonia and nitrite under 0.50ppm.  Also, use liquid testing such as the API Master freshwater test kit rather than the test strips.   
-Matt-