Bubble algae is one of the slowest problems in a reef tank. A few green marbles on one rock look harmless, and then a year later they are wedged between every coral. It is beatable, but most of the work is patience and not making it worse.
Disclosure up front: we make Bubble Bath coral dip, and it is labelled for bubble algae. I will cover it where it fits, alongside the methods most reefers use with or without it.
What bubble algae is
The common bubble algae in reef tanks is Valonia, often sold or discussed under the name Ventricaria ventricosa. Each bubble is a single, very large cell. That is why it looks so different from other nuisance algae.
How to identify it
- Smooth, shiny spheres, usually dark green, sometimes with a slight blue or silver sheen.
- Sizes range from a pinhead to a marble or larger.
- Grows in clusters on rock, often in crevices, under ledges and at the base of corals.
- Feels firm, like a water balloon. It does not have strands or fronds.
Some look-alikes are harmless or even wanted. Small green bubbles on a coral can be the coral itself (bubble corals have grape-like vesicles, for example). If it is attached to the rock and has no tissue around it, it is probably Valonia.
Why it spreads, and why popping makes it worse
Bubble algae almost always arrives on something: a frag plug, a piece of live rock or a snail shell. From there it spreads slowly across the rock work.
The common hobby advice is never to pop a bubble in the tank. When the cell ruptures, its contents go into the water and can settle and grow into new bubbles. Plenty of reefers have scrubbed a rock clean and found more bubbles on nearby rock a few weeks later. Treat every bubble as something to remove whole.
Manual removal
Manual removal is still the first step for most tanks. Done carefully, it works well on a small outbreak.
- Turn off powerheads and the return pump so anything released does not drift.
- Slide a toothpick, wooden skewer or blunt plastic tool under the base of each bubble and lever it off the rock.
- Lift it out with tweezers or catch it with a siphon hose running into a bucket.
- Work a few rocks per session, then do a water change.
- Recheck every week. Small bubbles you missed will show up as they grow.
Expect repeat sessions over weeks or months. Holdfasts left in the rock can regrow, so one clean pass is rarely the end of it.
Cleanup crew options
Emerald crabs
Emerald crabs (Mithraculus sculptus) are the most common bubble algae control. Many will pick the bubbles off rock. Results vary a lot by individual, and a well-fed crab may ignore them. As they grow, some will nip at corals or steal food, so keep an eye on them and be ready to remove one if it misbehaves.
Foxface rabbitfish
Foxface rabbitfish are reported by many reefers to graze bubble algae. Not every fish does. They also need a fairly large tank, and their dorsal spines are venomous, so handle with care during maintenance.
Neither of these is a guaranteed fix. Think of them as a way to slow regrowth after manual removal.
Nutrient control
Bubble algae can keep growing in tanks with low nitrate and phosphate, so nutrient control alone rarely clears it. It still helps. A tank with phosphate sitting high gives every algae an easier time, and regrowth after removal is slower in a stable, well-exported system.
- Test nitrate and phosphate, and aim for stable, low but non-zero levels.
- Avoid overfeeding and clean filter socks or floss on schedule.
- Run a skimmer, refugium or phosphate media as your system needs.
Do not chase zero. Bottoming out nutrients can trade bubble algae for dinoflagellates, which are far harder to deal with. See our guide to dinoflagellates vs cyano vs diatoms if brown film shows up while you are cutting nutrients.
Dipping removable rock and frags
If the bubbles are on a frag, a plug or a rock you can lift out, treating it outside the tank is the cleanest option. Nothing released in a container can reach the display.
Bubble Bath is labelled for bubble algae as well as animal pests. The directions are 1 part dip to 5 parts saltwater (1.026 sg) for exactly 1 minute. The product page says the algae disintegrates within days after the dip, so do not expect bubbles to vanish in the container.
- Pull obvious bubbles off whole before dipping.
- Agitate with a turkey baster during the minute, including crevices and the underside.
- Rinse in clean saltwater and dump the used dip down the drain.
- Rocks need enough dip to fully cover them, so this is most practical for small rocks, plugs and frags.
Dipping kills the copepods and other small life living on that piece. That is localized and expected, but it is worth knowing before you dip a large chunk of rock. For the full routine, see how to dip corals.
The cheapest prevention is dipping and inspecting every new frag. If you see a bubble on a plug, remount the coral on a new plug and throw the old one away.
In-tank options
When the bubbles are spread across rock that cannot come out, you are left with manual removal, a cleanup crew, nutrient control and in-tank treatment.
Bubble Bath can also be dosed in the display tank for nuisance algae. The dosing calculator on the Bubble Bath product page gives 1.5 to 2.5 mL per 10 gallons, twice a day. Remove carbon while dosing. The calculator notes that results show in 6 to 8 weeks, so this is a slow approach, not a quick knockdown. It works best combined with manual removal so you are not waiting on the dose to clear large clusters.
Other dips like Coral RX, ReVive or iodine are not aimed at algae. Our coral dip comparison covers what each one is for.
A realistic plan
- Confirm it is Valonia and not part of a coral.
- Remove bubbles whole with pumps off, a few rocks at a time.
- Pull out and dip any small rocks, plugs or frags that carry bubbles.
- Add an emerald crab or two if your tank suits them.
- Keep nutrients stable and low but not zero.
- Consider an in-tank dose if regrowth keeps up with your removal.
- Dip every new coral so it does not come back on the next frag.
Bubble Bath is sold at Coral's Coral.
Common questions
Should I pop bubble algae?
No. The common hobby advice is to remove each bubble whole, because a popped bubble releases its contents into the water and can start new bubbles elsewhere. Pry it off from the base with a toothpick or blunt tool and lift it out intact.
Do emerald crabs really eat bubble algae?
Many do, but not all. Results vary from crab to crab, and a crab with plenty of other food may ignore the bubbles. Larger individuals can also start picking at corals, so watch them.
Is bubble algae caused by high nutrients?
Not only. Bubble algae is usually introduced on rock or frag plugs, and it can keep growing in tanks with low nitrate and phosphate. Good nutrient control slows it down but rarely removes it by itself.
Can I dip live rock to kill bubble algae?
Yes, if the rock fits in a container. Bubble Bath is labelled for bubble algae at 1 part dip to 5 parts saltwater for 1 minute, and the algae breaks down over the following days. Dipping also kills the copepods living on that piece.
Can Bubble Bath be dosed in the display tank for bubble algae?
The tank dose is labelled for nuisance algae in general. The product page calculator gives 1.5 to 2.5 mL per 10 gallons twice a day, with carbon removed, and says results take 6 to 8 weeks.