Until you have a test kit, it is all a guessing game. Take a water sample to your lfs
and ask them to test it with a liquid reagent test kit. Your loss of fish and having to drive to the lfs
to have the water tested will end up costing more than the test kit.
The tank is probably not cycled. Unless you tested the water to ensure the cycle has completed, you can't be for sure. When you did the water change, did you clean the filter or do a deep gravel vac? Removing the wood and doing a large water change shouldn't be a big deal as long as you didn't disturb the bacteria in the gravel and in the filter. The tank needs to mature a bit longer before doing any drastic cleanings. Simple water changes won't do harm though.
Get the water tested and we can point you in the right direction. If all is clear and the tank is cycled (0 Ammonia and Nitrites with 10+ Nitrates) we can go from there. BUt if it itsn't, we can take appropriate steps with water changes.