Hi,
I wasn't able to start a new thread, so I'm posting here. I have a similar question as the original poster.
We got our daughter a 10 gallon tank, cleaned all the gravel and decorations (without soap of course), and added water conditioner to the water. The tank has a heater and a filter that moves the water. We did not do a fishless cycle originally. We let the tank run for a few days, got 2 glofish tetras, and added them to the tank. After about 3 hours they started to swim the to surface, with their mouths opening and closing at the surface. They both died within a 4 hour time period. We returned them, talked to the people at the store. They tested our water and everything looked fine. They thought that perhaps there wasn't enough oxygen. We got a moss ball, as well as an airstone, pump, and tubing and hooked that up and let it run for awhile. We got 2 new fish then, and they died after 7 hours. They had started swimming to the top, as well, after about 5 hours. We floated their bags when we got them for about 15 minutes, then added some of our water and let them sit for another 15 minutes, then added them to the tank.
What do you think caused them to die so quickly?
We have since emptied our tank, we got water and substrate from a friend who has an established, thriving tank. When I tested it last night, it showed 0 levels of ammonia and nitrites, and the nitrate reading showed about 20. PH was 6.2, hardness 300, Chlorine was 0, and alkalinity was the lowest reading. What should we do to maintain this water in order to get it ready for fish? We just put the water and substrate in yesterday.