Male bettas + gouramis blow bubbles at surface to build nest for eggs. Normal pre-breeding behavior.
Different from bubble blowing - fish gulping air at surface = LOW oxygen. Add aeration immediately.
Hatchetfish, killifish, splash tetras hover near surface. Normal.
Test water first - many "behavior" issues are actually water-quality problems. Use the water parameter checker to score your test results, the disease symptom matcher if you observe physical signs, or the general diagnoser to narrow further. Browse the disease database if illness is suspected.
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