Bubbles in aquarium water have multiple causes - some normal, some warning. Normal bubbles: 1) New water with dechlorinator - clears in 4-6 hours. 2) Filter return + powerheads create surface agitation - normal. 3) Plant pearling (CO2 oxygen bubbles in heavily-planted tanks during photosynthesis) - sign of healthy plant growth. 4) Cold water releasing dissolved gas as it warms in tank. 5) New tank degassing for first week. Warning bubbles: 1) Persistent foam on surface = high dissolved organic compounds (DOCs). Do 30% water change + run carbon. In reef tank, indicates overdue skimmer cup empty. 2) Constant micro-bubbles in tank = pump cavitation or sump intake drawing air. Inspect impeller seals. 3) Massive bubbles + cloudy water with foul smell = bacterial bloom + decaying organic matter. Immediate water change. Pearling vs problem: pearling stops a few hours after lights off; problem-bubbles persist. Surface tension film: oily slick + bubbles trapped underneath = protein film. Use surface-skimmer attachment on filter intake.
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