Cyanobacteria & Dinoflagellates: Reef Tank ID & Treatment
Not all reef tank nuisances are the same, and that matters a lot when it comes to treatment. Two of the trickiest, cyanobacteria and dinoflagellates, get confused with each other and with regular algae all the time. At Tropical Treasures in Cheyenne, telling them apart is the first question we ask, because the wrong approach can make one of them much worse.
This quick-reference guide will help you identify what you're actually looking at and choose a treatment that works without nuking the good life in your tank.
Cyanobacteria: the red slime 🔴
Cyano usually shows up as a slimy, dark red, maroon, or blue-green film that coats sand, rock, and gear, often trapping tiny oxygen bubbles. You can peel it off in sheets, and it has a distinct earthy smell. Despite the look, it isn't algae at all but a photosynthetic bacteria. It thrives in low-flow areas with built-up nutrients and old, weak lighting.
How to treat cyano 🧹
Cyano responds well to a multi-pronged approach: increase flow to dead spots, siphon out the slime during water changes, cut back feeding, and refresh aging light bulbs. Many reefers beat it with these steps alone. A short blackout period can help too. Chemical "red slime removers" exist, but use them carefully and only after improving the underlying conditions.
Dinoflagellates: the snotty strings 🟤
Dinos are the scarier of the two. They typically look like brown, stringy, snot-like strands full of trapped air bubbles, often with a slimy or web-like texture. They tend to appear in the afternoon and recede overnight. Unlike cyano, many dino strains explode when nutrients are too low, so the usual "starve it out" advice can backfire badly and even harm your livestock.
How to treat dinos ⚠️
Because some dinos are toxic to fish and corals, go slow and confirm the ID first, ideally under a microscope. Counterintuitively, the fix often means raising nutrients slightly, dosing beneficial bacteria, running UV sterilization, doing a few-day blackout, and boosting biodiversity with quality live rock or pods. Avoid huge water changes that crash nutrients further.
Cyano vs. dinos at a glance 🤔
The quick tell: cyano is a smooth, slimy red or blue-green sheet you can peel off; dinos are brown, stringy snot with lots of bubbles that comes and goes with the daylight. Cyano usually means too many nutrients, while a dino outbreak often means nutrients have bottomed out. That's why a microscope or a quick photo to an experienced reefer is worth it before you act. If you want to brush up on the numbers, check our reef tank water parameters resources first.
The bottom line 🐚
Identify before you treat. Cyano is usually a straightforward flow-and-nutrient fix, while dinos demand patience and the opposite instinct of starving them. When in doubt, slow down and ask for help. Bring a sample or a clear photo to Tropical Treasures or call 307-369-1118, and we'll help you pin down which pest you've got and a safe plan to clear it. Find more help on our Tank Buddy Blog.