Likely cause
Protein Foam / Surface Bubbles
Foam or bubbles on the surface usually come from a buildup of dissolved proteins, often linked to overfeeding or waste. A partial water change plus more surface agitation clears it, and cutting back feeding slightly helps prevent it from returning.
Why this happens
- A buildup of dissolved proteins, usually from overfeeding or excess organic waste.
- Low surface agitation lets foam accumulate instead of breaking up naturally.
- New tap water additives or medications can sometimes contribute temporarily.
What to do next
- Do a partial water change to remove the dissolved proteins causing the foam.
- Increase surface agitation with an air stone or by adjusting filter flow.
- Cut back feeding slightly, and remove any uneaten food promptly.
- Skim visible foam off the surface with a net or paper towel while addressing the underlying cause.
Frequently asked questions
Why is there foam on top of my fish tank?
It's usually a buildup of dissolved proteins from overfeeding or waste — a partial water change and more surface agitation typically clears it within a few days.