Reef Tank Cyanobacteria Removal Guide: Red Slime Causes
That maroon film creeping across your sand is not algae and will not respond to algae-control tactics. Cyanobacteria are photosynthetic bacteria that thrive where flow stalls and dissolved organics linger, and they double in mass every 12 hours under reef lighting. Reef cyanobacteria removal works only when you fix the underlying flow and nutrient problem alongside chemical treatment, otherwise the slime returns within a fortnight. This protocol from Gensou Aquascaping at 5 Everton Park covers the diagnostic, treatment and aftercare sequence we run on customer tanks.
Identify Cyano vs Dinoflagellates
Cyano is rust-red to dark maroon, slimy to the touch, and traps oxygen bubbles by mid-afternoon. It peels off rock in sheets when siphoned. Dinoflagellates are stringier, brown to gold, and snap back faster. Misidentifying the two leads to wasted antibiotic doses, because Chemiclean does not touch dinos.
Diagnose the Flow Dead Spots
Drop a pinch of dry food into the display with the lights off. Wherever it settles instead of swirling, that is your cyano nursery. Common culprits: behind aquascape pillars, under the sand bed near the overflow, and along the front pane where wavemakers shoot past. Reposition powerheads to break up laminar flow before any chemical treatment — wavemakers and gyre pumps live in the aquarium equipment range and a single repositioned wavemaker often fixes mild outbreaks alone.
Address Nutrient Imbalance
Cyano explodes when nitrate sits above 10 ppm and phosphate above 0.1 ppm, especially when the ratio is skewed. Test both with hobby kits and aim for nitrate 2-5 ppm, phosphate 0.03-0.05 ppm. Drop bioload by feeding less, replace mechanical socks every two days, and run fresh activated carbon. Counter-intuitively, very low nutrients also feed cyano because corals starve and shed organics — chasing zero is a trap.
Manual Removal Before Dosing
Siphon every visible patch with a turkey baster and fine tubing during a 10 per cent water change. Skip bleaching the rocks; the cyano under the sheet you just lifted will regrow before the antibiotic loads. Replace any clogged filter sock and clean the skimmer cup. This step alone reduces the antibiotic dose impact on the biofilter.
Dosing Chemiclean Correctly
Chemiclean is erythromycin-based and clears most outbreaks in 48 hours. Dose 4 grams per 200 litres with skimmer off and ozone disabled, run heavy aeration through an air stone, and keep lights on for the full 48 hours so the bacteria stay metabolically active when the antibiotic hits. Perform a 25 per cent water change at the 48-hour mark and run fresh carbon for three days. Repeat dosing creates resistant strains — if a second round fails, switch to UltraLife Red Slime Remover or escalate to lanthanum chloride for the phosphate driver.
Salt Mix and Top Off Quality
Some salt batches carry trace phosphate that quietly feeds cyano. Test freshly mixed saltwater straight from the bucket; if phosphate reads above 0.03 ppm out of the box, switch brands. RODI top-off must be genuine zero-TDS — Singapore PUB tap pushed through a single-stage filter does not qualify. Quality salt mix and RODI cartridges live in the marine saltwater range.
Light Spectrum and Photoperiod
Cyano photosynthesises most efficiently in the red and far-red bands. Drop the red channel on the reef LED to 20-30 per cent during outbreak weeks and tighten the photoperiod to 8 hours instead of the usual 10-12. Keep blues for coral health. Restore the spectrum gradually over two weeks once the slime clears.
Long Term Prevention
Bi-weekly 10 per cent water changes, monthly skimmer cup cleaning, replacing filter floss every three days and keeping a refugium with chaeto are the boring habits that prevent recurrence. A turkey baster blast across the rockwork once a week keeps detritus from settling. The reef hobbyists who never see cyano are the ones who automate consistency, not the ones with the most expensive equipment.
Related Reading
emilynakatani
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
