Brown Algae Fish Tank Complete Guide: Diatoms and Silicates
That dusty brown film coating glass and substrate three weeks into a new setup is not algae in the botanical sense — it is a diatom colony, a single-celled organism with silica shells that thrives in maturing tanks. This brown algae fish tank complete guide explains why diatoms appear, how Singapore’s PUB water silica content drives them, and the practical removal steps. Gensou Aquascaping at 5 Everton Park sees the brown bloom in almost every new tank before month two, and it always resolves with the right approach.
Diatoms Are Not True Algae
Diatoms belong to the Bacillariophyta group, distinct from green algae. Their cell walls are made of silicon dioxide — glass, essentially — which gives them the characteristic dusty appearance that wipes off easily. They need dissolved silica, nitrate, phosphate and light to grow. In a mature tank, green algae and plants outcompete them. In a new or imbalanced tank, diatoms flourish first.
Why New Tanks Get Brown Algae
Three conditions converge in new setups:
- Fresh substrate and hardscape leach silicates for 4-8 weeks.
- The tank has few plants or poorly established ones not yet consuming nutrients.
- Lighting is often over-spec from day one, chasing future plant needs.
The diatom film is actually a positive early signal — it means the tank is cycling nutrients. It almost always disappears on its own once the ecosystem matures.
PUB Water and Silicate Input
Singapore PUB tap water typically tests around 3-5 mg/L dissolved silica, comparable to most reservoir-sourced supplies worldwide. Water from NEWater filtration runs lower but is not commonly dosed into aquariums. Substrate choice matters more than tap water — silica sand, lava rock and cheap filter gravel release silicates for months. Inert aqua soil and HDPE-based substrates contribute almost nothing.
The Wait-It-Out Approach
For tanks younger than 8 weeks, the standard advice is patience. Wipe glass weekly with a magnetic cleaner or microfibre pad, siphon the substrate during water changes, and leave the biofilm on hardscape if livestock grazes on it. Most brown algae clears itself by week 10-12 as plants mature and nutrient balance settles. Chemical interventions at this stage usually make things worse by killing establishing bacteria.
Otocinclus and Nerite Snail Grazing
Two local livestock options handle diatoms efficiently. Otocinclus catfish graze brown algae aggressively — a group of 4-6 in a 60 L tank clears visible film within days. Buy them from Iwarna Aquafarm or Qian Hu where batches tend to be healthier than generic LFS stock; expect SGD 6-10 each. Nerite snails (horned, zebra, black racer) graze glass relentlessly and cost SGD 3-5 each. Both need a mature tank with ongoing biofilm; do not introduce on day one.
Reducing Silicates in Established Tanks
If diatoms persist past 12 weeks, reduce inputs:
- Replace silica-rich substrate with aqua soil or Seachem Flourite if feasible.
- Add phosphate-silicate remover resin (Seachem PhosGuard, SGD 35 on Shopee) to filter media for 2-4 weeks.
- Reduce photoperiod to 6 hours daily.
- Do 30 per cent weekly water changes to dilute leaching nutrients.
Address all four simultaneously rather than piecemeal.
Light Intensity and Spectrum Factors
Diatoms prefer lower light intensity than true algae, which is why they colonise shaded areas first — under driftwood, behind plants, in substrate crevices. Cranking up lighting to combat them backfires; stronger light fuels green algae layered on top. Instead, dial lights to 40-50 per cent intensity for the first two months, then ramp up as plants fill in. A timer setting of 6 hours daily suffices during establishment.
Filter and Circulation Checks
Dead spots let diatoms accumulate beyond normal. Aim for gentle flow across every glass surface — a spray bar at the rear wall or a directed HOB outflow usually covers a 60-90 cm tank. Replace mechanical filter floss weekly during an active bloom; it captures silica-bound particulates. Never rinse biological media in tap water as PUB chloramine destroys the bacterial colony that indirectly competes with diatoms for nitrogen.
When Brown Algae Signals a Real Problem
Persistent brown algae past three months in an established planted tank points to underlying imbalance: insufficient CO2 for planted growth, nitrate spikes from overfeeding, low circulation, or failing plants releasing nutrients. Investigate rather than treat symptoms. A single audit session at Gensou Aquascaping usually identifies the root cause within 20 minutes of water tests and visual inspection.
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emilynakatani
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