| What It Is | Single-celled bubble macroalga |
| Looks Like | Shiny green spheres/bubbles on rock |
| Main Cause | Hitchhiker; nutrients help it spread |
| Difficulty | Easy to remove, easy to spread |
| Best Fixes | Careful manual removal + emerald crabs |
Overview
Bubble algae (Valonia or Ventricaria) shows up as glossy green orbs on your rock. The famous warning is real but often misunderstood: each “bubble” is essentially one giant cell, and if it ruptures it can release spores — so the goal is to remove bubbles without popping them into the tank. It’s not aggressive like Aiptasia, but left alone it multiplies and shades rock.
How to Identify It
Round to teardrop shiny green (sometimes silvery or dark) bubbles, from pinhead to marble sized, singly or in grape-like clusters, firmly attached to rock. The mirror-like sheen and perfect sphere shape are unmistakable — nothing else in the tank looks like a little green water balloon.
How to Get Rid of It
- Manual removal, intact — gently work each bubble off the rock whole, or lift the rock out and remove them over a bucket. Try to get the attachment point without bursting the sphere. If one pops, siphon the area.
- Emerald crabs (Mithraculus sculptus) — the classic bubble-algae grazer; many will pick and eat Valonia. Results vary by individual crab, so pair them with manual removal.
- Siphon while you pluck — remove bubbles with a siphon running nearby so any released spores get pulled out rather than settling.
- Keep nutrients moderate — won’t remove existing bubbles, but slows how fast new clusters form.
Prevention
Inspect and, where practical, remove bubble algae from new rock and frag plugs before they go in — it’s a hitchhiker. An emerald crab or two as standing clean-up crew keeps stragglers in check. Deal with a cluster while it’s small; a dozen bubbles is a five-minute job, a covered rock is not.
What Doesn’t Work
Popping bubbles in the tank “to pop them all”: the one thing everyone warns against — you may be seeding spores. Remove whole. Relying on the crab alone: emerald crabs are inconsistent; some ignore Valonia entirely. Ignoring it: slow-spreading isn’t no-spreading.