I am SO upset! I've had a 29 gallon, heavily planted, up and running with the same 4 fish for a year. A flame gourami, 2 otos and a siamese algae eater. I've not changed anything in months. The plants do a good job of keeping nitrates down so I usually top off the tank and then vacuum about once a month. I vacuumed with the same vacuum I always use about 30% of the water 3 days ago. I used stress coat to dechlorinate. Other than poking a few loose plant roots back in to the sand I changed nothing. Today I have a dead oto, a dead SAE and my gourami is definitely going to die. The last remaining oto is so hard to find that he may be dead soon too. What did I do to cause this mayhem!!!?! .25 ammonia, 0 nitrite, 0 nitrate. The only thing I didnt test was pH but I'm always right at 7.2 so unless disturbing the sand caused something to be released I am at a total loss. THe fish seemed fine yesterday and the day before. The gourami started being weird today and thats when we found the recently dead oto and algae eater. No white marks, not fungus, no clamped fins, no hemorraging, no holes, no missing scales. Perfectly normal looking fish except for the dead part.