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Beating Reef Tank Algae and Pests

By The Coralkin Team · written & researched by reef keepers🔍 Keeper-reviewed & fact-checked

🐠 The short version: most reef “algae problems” are water and maturity problems. A brown “uglies” phase in a new tank is normal and passes. For the rest — cyano, dinos, hair algae, aiptasia — the fix is almost always the same shape: test first, balance nutrients (low, not zero), improve flow, manually remove, and let a cleanup crew help. There’s rarely a magic bottle.

🔧 Start by testing — most outbreaks trace to nutrients being too high or too low. Check against the parameter chart, and right-size your janitors with the cleanup-crew calculator.

First: the “uglies” are normal

If your tank is young and covered in brown film, that’s diatoms — the “uglies” — and it’s a rite of passage, not a failure. New tanks have fresh surfaces and silicates that diatoms bloom on; they fade on their own as the tank matures and a cleanup crew gets to work. Don’t scrub obsessively or reach for chemicals. Patience is the treatment.

The nutrient balance behind (almost) everything

Here’s the counterintuitive core of pest algae: it’s driven by nutrients being out of balance in either direction.

  • Too high (excess nitrate/phosphate from overfeeding or weak export) feeds hair algae and cyano.
  • Too low (nutrients chased to zero) starves corals and hands the tank to dinoflagellates.

So the target is low but not zero — roughly nitrate 2–15 ppm, phosphate 0.03–0.10 ppm. This is exactly why chasing zero nutrients backfires. Test before you act.

The usual suspects, and how to beat them

Cyanobacteria (red/maroon slime). Not a true algae — a bacterium that films low-flow, nutrient-rich spots. Improve flow, tidy up nutrients and overfeeding, and manually siphon it out. Treat the cause; a “red slime remover” alone just delays the return.

Dinoflagellates (brown, snotty, bubbly strands). The “too clean” pest. If nitrate/phosphate read zero, gently bring them back up to a healthy low level; dinos struggle to compete once other life has nutrients again. Go carefully — some dinos are toxic, so avoid disturbing big blooms into the water column.

Hair algae (green turf). Feeds on nutrients and light. Manually pull out what you can, tighten nutrient export, check your lighting isn’t excessive or a bulb long overdue, and add grazers — snails now, and a tang later only if your tank genuinely suits one (not a small-tank fish). It’s a marathon.

Aiptasia (little glass anemones). A stinging pest that harms corals. Never cut or crush it — that scatters it into dozens. Kill individuals with a dedicated aiptasia treatment, and/or add a natural predator like peppermint shrimp or a filefish. Persistence wins because survivors multiply.

Your cleanup crew is support, not a cure

A well-chosen cleanup crew (snails, hermits, and specialists like peppermint shrimp for aiptasia) grazes film algae and detritus and keeps a mature tank tidy — but it supplements good husbandry, it doesn’t replace it, and overstocking one just starves it. Size it sensibly with the cleanup-crew calculator, and see the cleanup crew guide for who eats what.

The honest takeaway

Reach for the test kit before the chemical. Get nutrients into the low-but-not-zero band, keep flow and export healthy, remove pests by hand, add the right janitors, and give a young tank time to mature. Do that and algae stops being a crisis and becomes routine maintenance.

Sources & further reading

Common questions

Why does my new reef tank have brown algae everywhere?

That is the diatom "uglies" phase, and it is completely normal in a young tank. Diatoms bloom on the fresh surfaces and silicates of a new setup, then fade on their own as the tank matures and a cleanup crew goes to work. Do not panic or over-scrub — patience is the fix.

How do I get rid of hair algae?

Starve it and graze it. Hair algae feeds on nutrients, so manually remove what you can, tighten nutrient export and lighting, and add grazers (snails, and for larger tanks a tang once the tank suits one). It is a marathon, not a chemical quick-fix.

Why did dinoflagellates appear when my water is very clean?

Because it is too clean. Dinoflagellates thrive when nitrate and phosphate bottom out, outcompeting other life in nutrient-starved water. A common first step is to bring nutrients back up to a healthy low level rather than driving them lower.

How do I remove aiptasia?

Do not cut or crush it — that spreads it. Use a dedicated aiptasia treatment to kill individual pests, or add a natural predator such as peppermint shrimp or a filefish. Persistence matters, because survivors multiply.

Is cyanobacteria the same as algae?

No — the red or maroon slime is cyanobacteria, a bacterium, not a true algae. It films over sand and rock in low-flow, nutrient-rich spots. Improve flow, tidy up nutrients and manually siphon it out; treat the cause, not just the slime.

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