How to Get Rid of Brown Diatoms Permanently
A dusty brown coating on the glass, substrate and plant leaves — brown diatoms are often the first algae problem a new aquarium owner faces. The good news is that diatom blooms are almost always temporary. The frustrating part is that they look terrible while they last. This guide from Gensou Aquascaping at 5 Everton Park, Singapore, explains how to get rid of brown diatoms permanently by tackling the root cause rather than just wiping them away.
What Are Brown Diatoms?
Diatoms are microscopic single-celled algae with silica-based cell walls. The brown, powdery film they create is technically not “algae” in the green-plant sense — diatoms belong to a separate group entirely. They thrive on dissolved silicates in the water, which are abundant in new tanks where fresh substrate, new silicone sealant and uncycled filter media all leach silica. Their brown colour comes from the pigment fucoxanthin, which masks the chlorophyll underneath.
Why New Tanks Get Hit Hardest
Nearly every new aquarium experiences a diatom bloom within the first two to eight weeks. Fresh aquasoil, gravel and sand all release silicates as they settle in. Tap water also contains dissolved silica — Singapore’s PUB water typically carries 5-15 ppm, which is enough to fuel diatom growth. Low light, unstable nutrient cycling and immature biological filtration create the perfect storm. Established tanks with mature filter colonies and stabilised substrate rarely have diatom issues unless something disrupts the equilibrium, like a major substrate change or extended blackout.
Immediate Removal
Brown diatoms wipe off glass easily with a magnetic cleaner, algae pad or even a soft cloth. They are far less adherent than green spot or black beard algae. On plant leaves, a gentle rub between your fingers dislodges them. During water changes, siphon the substrate surface to remove settled diatom film — a gravel vacuum works perfectly. These steps make the tank look better immediately, but the diatoms will return within days if the underlying silicate source remains.
Biological Clean-Up Crew
Otocinclus catfish are the gold standard for diatom removal. A group of three in a 60-litre tank can clear a moderate diatom bloom within a week. They graze methodically across glass, leaves and hardscape. Nerite snails also consume diatoms enthusiastically and leave attractive spiral trails in the film as they work. Amano shrimp contribute as well, though they prefer other food sources and tackle diatoms more as a secondary diet. Introduce your clean-up crew once the tank has completed its nitrogen cycle — adding them too early exposes them to ammonia and nitrite spikes.
Addressing the Silicate Source
Once the initial silicate leaching from new substrate and hardscape subsides — typically after six to twelve weeks — diatom blooms diminish naturally. You can accelerate this by performing frequent water changes (two to three times weekly at 30%) during the first month to dilute dissolved silicates. If your tap water is high in silicate, using RO water for changes eliminates the resupply. Silicate-absorbing filter media, such as PhosGuard or JBL SilikatEx, placed in a media bag inside your filter removes dissolved silica directly. A 250 ml bag costs around $12-18 and lasts four to six weeks in a 100-litre tank.
Light and Nutrient Balance
Diatoms actually prefer low-light conditions, which is why they dominate in new tanks before higher plants establish and compete for nutrients. Increasing your lighting period to 8 hours and intensity to moderate levels encourages plant growth that out-competes diatoms for available nutrients. In planted tanks, ensuring healthy plant mass through adequate fertilisation and CO2 is the most effective long-term prevention. Fast-growing stem plants like Hygrophila polysperma and floating plants like Salvinia are particularly effective nutrient competitors.
Long-Term Prevention
Maintain a consistent water change schedule of 25-30% weekly. Keep the tank well-planted and avoid prolonged periods with lights off, which paradoxically favours diatoms over green plants. If you are running a fish-only tank, consider adding a few hardy plants — even just Java fern and anubias attached to driftwood — to introduce biological competition. Monitor silicate if you suspect your water source is the ongoing contributor; a silicate test kit from Salifert or Hanna costs around $15-25 and gives you clear data.
When Diatoms Signal a Bigger Problem
In an established tank, a sudden reappearance of diatoms often indicates a disruption: a filter cleaning that removed too much beneficial bacteria, a new batch of substrate or an extended power outage that crashed the biological cycle. Address the root disruption rather than just fighting the symptom. If diatoms persist beyond three months in a fully cycled, well-planted tank, investigate silicate levels in both your tap water and substrate. The team at Gensou Aquascaping has helped many Singapore hobbyists troubleshoot persistent algae — bring your water test results and photos for a targeted assessment.
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emilynakatani
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