White Algae Fish Tank Guide: Mould or Biofilm ID
White fuzzy growth in a new aquarium scares beginners into thinking their tank has crashed — but true “white algae” is almost never algae at all, and the correct identification decides whether you do nothing, siphon it out, or treat for a genuine problem. This white algae fish tank guide from Gensou Aquascaping at 5 Everton Park covers the three possibilities — driftwood biofilm, fungal growth on leftover food, and actual white cottony saprolegnia — plus how to tell them apart in under five minutes. Singapore’s warm tap water at 28-30°C accelerates both biofilm formation and fungal bloom on any new tank setup, so every local aquascaper sees at least one white fuzzy phase within the first month of a new build.
Driftwood Biofilm Is The Most Common Culprit
Fresh driftwood — spiderwood, red moor, Malaysian, seiryu-adjacent wood from C328 Clementi, Aquariumwest or Green Chapter — almost always grows a slimy white-to-translucent biofilm within 5-14 days of submersion. It looks like cobwebs or snot draped across the wood surface and indicates bacteria and fungi breaking down lignin and sugars in the wood. This is harmless, will stop within 2-4 weeks, and gets grazed by Amano shrimp, Nerite snails and otocinclus if present. Do nothing except siphon loose pieces during water changes.
Fungal Growth On Leftover Food
White fuzzy growth specifically on dead plant matter, leftover fish food pellets in corners, or dying leaves is true saprophytic fungus. It is a cleanup signal: your tank has uneaten food or decaying material that the biofilter is not keeping up with. Remove the food residue immediately, siphon the affected area, reduce feeding to one small pinch twice daily, and the fungus clears within a week. At 29°C, fungi multiply roughly twice as fast as in temperate tanks, which is why Singapore hobbyists see it more than UK forums imply.
Saprolegnia: The One To Worry About
If white cottony growth appears on a living fish — around the mouth, gills, fin edges, or on fish eggs — that is saprolegnia, a true water mould, and demands action. It opportunistically colonises stressed or injured fish in warm, poorly-oxygenated water. Raise dissolved oxygen with extra aeration, drop temperature 2°C if possible via fan-assisted evaporation or a small chiller, and treat with methylene blue (SGD 8-14 at Y618 and Qian Hu) for eggs or formalin/methylene blue baths for adults. Seachem ParaGuard and Waterlife Myxazin are the next step for stubborn cases.
Tell Them Apart In 5 Minutes
Poke it with a skewer. Clear, stringy, clings to wood and pulls off in strands? Biofilm. Dense white cotton ball on a dead item, localised? Saprophytic fungus. Cotton on a fish or in an obvious patch on a living plant? Saprolegnia — act. Pale white patches on glass that scrape off crunchy? That is calcium or mineral deposit, not algae at all. Each path leads to a different action, so spend the five minutes observing first.
Why New Tanks Grow So Much Biofilm
A freshly-set-up tank has abundant dissolved organic carbon, minimal established microfauna, and unclaimed surface area. Bacteria, fungi and protists colonise every inch until equilibrium reaches around week 3-5. Adding Amano shrimp early (week 2) or a nerite snail or two gives biofilm predators a head start. Feeding sparingly during this phase — less than you think — speeds equilibrium significantly; overfeeding extends the fuzzy phase by weeks.
Flow and Oxygenation Help Every Case
Dead spots grow biofilm and fungus faster. Aim for 5-10x turnover via your canister or hang-on filter, keep surface agitation strong enough to break the surface film but not violent, and add a circulation pump in larger tanks. Singapore’s warm water holds less dissolved oxygen at saturation than cold water — roughly 7.6 mg/L at 29°C versus 8.8 mg/L at 22°C — so aeration matters more here. A cheap ISTA air pump with a wooden airstone overnight (SGD 20-35) keeps oxygen high during the lights-off period when plants consume rather than produce.
Spot-Treat Only When Necessary
For localised fungal patches on hardscape that bother you visually, a 3% hydrogen peroxide spot-dose at 10 ml per 50 L, filter off and lights off for 15 minutes, clears the area within 24 hours. SGD 3-4 at Guardian or Watsons. Do not treat whole-tank for biofilm — you kill the beneficial biofilm on filter media too and trigger a mini-cycle. For fish-borne saprolegnia, skip H2O2 and go straight to methylene blue or a dedicated antifungal dip.
Prevention For The Next New Tank
Pre-soak driftwood for 2-4 weeks in a bucket with daily water changes before introducing to the display — biofilm grows and dissipates offline, sparing the display tank the visible mess. Scrub wood vigorously under running tap to remove loose surface material, then pour boiling water over it for 10 minutes if the wood is dense enough to handle the shock. Rock hardscape requires no such prep but still benefits from a scrub to remove clay and dust.
When To Actually Get Worried
A fuzzy tank in weeks 1-3 is normal. A fuzzy tank at week 8 means husbandry is off — usually overfeeding, an underpowered filter, or an unvacuumed substrate hoarding detritus. Test ammonia and nitrite to confirm the cycle is stable, check filter flow hasn’t dropped from clogging, and audit feeding honestly. Persistent fuzz past month three is always a cleanup-crew and feeding issue, never a mystery.
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Still Have Questions About Your Tank?
Drop by Gensou Aquascaping — most walk-in questions get answered in under 10 minutes by someone who has set up hundreds of tanks.
5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
