Posted by Jean Newton on April 15, 2004

Q: What do the bubbles mean that form on top of a filterless fish tank?

Some say the fish need more oxegyn. Some say it is an indication that the fish are breathing.

What do you say?

A: I've never been entirely clear myself, why one has bubbles one time and not another in an aquarium. I do think it has to do with material in or on the water that is cohesive (sticks together) and forms these bubbles. I also think there needs to be some water movement or agitation for these bubbles to form; your pump's action is probably making it possible for the bubbles to form but is not the ultimate cause. Although many think immediately of pollution, this is definitely not ALWAYS the case. I'd take my cue from your fish; if they're acting normally, have good color and not breathing with greater urgency (their gill covers moving more quickly than usual), I'd not worry. One thing to be careful of is not overfeeding. This can leave uneaten food in their tank and may cause some problems - whether in the form of bubbles or just yucky water, I really can't say. Good luck with your fish.

John Wiessinger ( April 16, 2004)