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Algae Identification & Control: BBA, Diatoms, Green Spot, Hair
1) Diagnose First: Species, Symptoms & Root Causes
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Before you fight algae, identify it. Every genus blooms for a reason, and treatment that crushes one type feeds another if the underlying cause remains. A reliable workflow: observe → test → correct → clean → prevent. Start with morphology. BBA (Audouinella) forms black/grey tufts on leaf edges, wood, and outlets; it feels coarse and resists rubbing. Diatoms dust new glass and hardscape with a brown film that wipes off easily. GSA appears as hard, circular green dots on slow leaves and glass that require a razor to remove. Green hair/filamentous algae make soft, threadlike mats that snag on moss and stems; green water is a pea‑soup bloom of free‑floating algae that turns the whole tank opaque.
Measure what matters. Use a liquid kit (see testing guide) to confirm ammonia, nitrite, nitrate, phosphate, and pH/KH. In planted systems, CO₂ stability is just as critical. A drop checker should trend lime‑green around lights‑on, and the pH‑drop method (see CO₂ tuning) verifies you’re consistently hitting ~1.0 pH drop from fully degassed water by the time full light begins.
Trace the trigger. Algae rarely means “too many nutrients.” Far more often it signals instability: fluctuating CO₂, sudden photoperiod/intensity jumps, clogged mechanical filtration (see maintenance), decaying leaves left in the tank, or poor flow that leaves dead zones. In new tanks, immature biofilms let diatoms dominate until competitors establish. In low‑tech builds, long photoperiods with weak flow invite hair algae on slow tissues.
Build a response plan. (1) Stabilize environment: consistent CO₂, steady photoperiod (6–7 hours while troubleshooting), and adequate but not violent flow across all leaves. (2) Remove biomass: manual tease‑out, razor glass, cut damaged leaves, siphon the debris, and run a short‑term polishing pad in a HOB/canister for 24–48 hours. (3) Starve/target the specific genus with nutrient/light corrections and—only if needed—spot treatments. (4) Prevent: resume a predictable maintenance cadence and keep filters clean so mulm doesn’t decay into fresh algal fuel.
2) Black Beard/Brush Algae (BBA): Stabilize CO₂ & Targeted Removal
BBA is the “CO₂ truth‑teller.” It anchors on hardscape and leaf edges when carbon availability fluctuates—especially when high light outpaces stable CO₂ or when flow doesn’t deliver CO₂‑rich water across the entire scape. Fluctuations can be weekly (dirty impeller, clogged pre‑filter) or daily (CO₂ starts too late, needle valve drifts, or surface agitation degasses).
Fix fundamentals first. Aim for a consistent ~1.0 pH drop from degassed water at lights‑on; start gas early enough (often 60–90 minutes pre‑lights) and ensure even distribution (full‑length spray bar or well‑placed lily pipe). Reduce surface agitation while keeping an oily film off the top—skimmers help. Trim or remove leaves encircled by BBA; they seldom recover.
Targeted removal. After a water change, briefly turn off filters/pumps. Spot‑dose 3% hydrogen peroxide or a liquid carbon (glutaraldehyde‑based) with a syringe directly on BBA tufts; wait 3–5 minutes, then restore flow. Expect tufts to turn pink/grey over 24–72 hours and shrimp/otocinclus to graze the weakened patches. Repeat weekly on remnants. Avoid blanket overdosing; protect livestock and beneficial bacteria.
Longer‑term prevention. Keep mechanical stages clean (prefilter weekly, canister/HOB pads 2–4 weeks), verify CO₂ at every rescape, and don’t chase extremely high PAR unless your flow and CO₂ delivery are dialed. Consider switching to a finer diffuser or inline atomizer for more uniform microbubbles, and validate the pH drop after any hardware change.
3) Diatoms & Green Spot Algae (GSA): Silicates, Phosphate & Light
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Diatoms are usually a new‑tank problem. Silicates from new sand, tap water, or leaching plastics fuel their brown dust until biofilms and plants occupy those niches. What to do: reduce photoperiod to 6 hours, wipe the dust during water changes, add flow, and wait 2–6 weeks. Otocinclus and nerite snails are excellent helpers. If your tap is high in silicate, a small RO/DI blend can shorten the phase.
GSA (green spot algae) forms hard dots that resist wiping. It correlates strongly with low phosphate under bright light on slow leaves (anubias, buce, older sword leaves). Raise PO₄ to ~0.5–2.0 ppm in high‑light tanks (and keep it stable), increase flow over problem leaves, and reduce photoperiod slightly while you correct the deficit. Scrape glass with a razor; for anubias/buce, remove the leaf if it’s peppered—the plant will push clean growth once PO₄ is corrected.
Distinguish from GDA. Green dust algae (GDA) coats glass in a uniform green film that comes back quickly if you wipe it early. The trick is to let it complete a life cycle: leave it 10–14 days, then wipe and water‑change; repeat if needed. Stable nutrients and photoperiod help prevent recurrence.
Signal vs noise. A little GSA on old leaves isn’t failure—it’s a maintenance reminder. If you’re fighting both GSA and diatoms, you likely have an under‑filtered or immature system; service filters, verify flow paths, and keep up water changes while plants establish.
4) Green Hair/Filamentous & Green Water: Nutrient Balance & Flow
Green hair/filamentous algae thrive when fast light and nitrogen (especially ammonia spikes from detritus or new substrate) meet slow plant uptake or weak flow. They tangle in moss and stem tips, then shade new leaves. Green water is different: a free‑floating bloom that turns the water itself opaque, often after deep rescapes, substrate disturbance, or strong sun.
Hair algae control. First, remove bulk biomass: twirl strands around a toothbrush, snip moss edges, and siphon. Reduce photoperiod to 6 hours temporarily, and ensure vigorous but even flow. Keep filters mechanically clean so they don’t leach dissolved organics. Dose a balanced macro/micro schedule so plants aren’t starved—algae exploit inconsistency more than abundance. Spot‑treat stubborn clumps after a water change with diluted peroxide or liquid carbon; avoid coating mosses repeatedly or you’ll burn them.
Green water fixes. Large water changes help but blooms rebound if the trigger remains. The cleanest cure is a UV sterilizer for 3–7 days—install inline on a canister return or as an internal unit, then remove or run intermittently once clear. Alternatively, a full blackout (3 days, no peeking, air stone on) followed by filter maintenance can reset the system. Address root causes: strong sun through windows, deep substrate disturbances, and inconsistent CO₂/light schedules.
Systemic prevention. Keep a simple weekly routine: 30% water change; skim detritus from open areas; clean pre‑filters; inspect leaves and prune early; and verify CO₂ stability at lights‑on. In low‑tech tanks, maintain modest photoperiods and lean dosing; in high‑tech tanks, prioritize even flow over extreme PAR—plants use light you can actually feed with CO₂ and nutrients.
FAQ
Why did BBA appear right after I increased light?
Because higher light increases demand for CO₂. If CO₂ concentration and distribution aren’t raised and stabilized to match, BBA exploits the imbalance.
How do I get rid of diatoms fast?
Manual wipe/siphon, shorter photoperiod, better flow, and patience. In new tanks they usually fade within a few weeks; RO/DI blending can help if silicate is high.
Is phosphate the cause of algae?
No. Low phosphate under bright light often triggers GSA. Stable, adequate nutrients paired with good maintenance prevent more algae than ‘starving’ the tank.
Next reads: Lighting Explained • CO₂ Systems & Tuning • How to Test Your Water • Water Changes & Gravel Vacuum
Labels: Algae Control, Planted Tanks, Beginner Guide, Maintenance