How do I get rid of dinos / dinoflagellates, cyano, diatoms in a reef tank? | SR FAQ #1

The single most frustrating problem for reef keepers is persistent outbreaks: slimes, diatoms, cyano, and especially dinoflagellates. If you want to know how to get rid of dinoflagellates in reef tank without tearing everything down, focus on three things: diagnosis, restoring a healthy microbiome, and controlling light and flow. This walkthrough takes you through the steps, tools, and timelines that actually work.

Quick Links: 

Chemiclean
TBS Ultra live Sand
KZ' Cyano Clean
Copepods
Hang on UV
Hobby grade Inline UV
Commercial grade inline UV
Mack's reef...Dinoflagellates support group!
Serious Reefs Biome Cycle (The ounce of prevention)
SR Podcast 23 ways to beat dinos!

*These links are provided as a quick way to find the items discussed in this video. Serious Reefs earns a small commission on some links when they’re used. Using them is a convenient, free way to support what we do here. Thank you.

Quick diagnosis: is it dinoflagellates or something else?

Before trying any dramatic remedies, identify what you’re facing. Different nuisances need different fixes.

• Cyano: often stringy, maroon to purple, typically responds to chemical cleaners like Chemiclean.

• Diatoms: brown dusting, common in new tanks. Often goes away on its own

• Dinoflagellates (dinos): often slimy mats or bubbly strings that come and go with light cycles, can be persistent and time alone is often not the solution

Step 1 — Try a targeted solution for cyano: Chemiclean.

If you suspect cyano, a targeted chemical treatment can often clear it quickly. Use a product designed for cyanobacteria like Chemiclean and follow directions. This is a low-effort first try that can save a lot of time and frustration if it works,

Using Chemiclean for Cyanobacteria in Reef Tanks

Chemiclean is widely believed to function as an antibiotic that can resolve bacterial issues like cyanobacteria (cyano) in reef tanks. Problem is often gone within 24 hours.

There has long been a belief in the hobby that Chemiclean only treats the symptoms of cyano rather than the root cause, meaning the problem will simply return once treatment stops. In some cases, that is true. If the cyano rapidly returns after treatment, it likely means the underlying conditions that allowed it to thrive are still present.

However, that is not always the case. If Chemiclean eliminates the cyano and it does not quickly return, the problem was likely a bacterial imbalance in the tank. In those situations, the antibiotic effectively treates the root cause of bacterial imbalence by reseting the microbial playing field and allows the system to re-establish a healthier balance. In our experience with cyano, this has been the outcome in roughly 90% of cases, with generally positive results.

That said, microbial outcomes in reef tanks can never be guaranteed. We cannot fully control the microbiome, only influence it. Occasionally, resetting the microbial environment can lead to new issues as the system finds a new equilibrium.

The reason we often suggest starting here is simple: diagnosis matters. If the issue is truly cyanobacteria, Chemiclean can often resolve it quickly and safely. But if the problem turns out to be dinoflagellates (dinos) instead, the treatment approach is far more complex and requires a very different strategy. Confirming whether you are dealing with cyano or dinos early on can save a lot of time, frustration, and unnecessary interventions.

If you prefer a gentler approach, you can try KZ’s Cyano Clean. It is widely believed to work by introducing beneficial bacteria that outcompete the cyanobacteria. This approach typically takes weeks rather than producing results in 24 hours, but it is arguably a lower-risk method.

Step 2 — Find a resource for asking questions

If you have determined what you are dealing with is dinos / dinoflagellates the first move is join a community whose sole focus solving problems like yours. Mack's reef...Dinoflagellates support group! is the best one out there.

Step 3 — Seed the tank: fix the sterile environment

The SR team strongly believes that dinoflagellates are present in most reef tanks and only become problematic when they fall out of balance with the other organisms in the system. Fixing that microbiome is our frontline approach.

Many persistent ugly stages stem from a lack of microcrustaceans or natural ocean based stains of bactera. If your sump, sand bed, or rockwork is what hobbyists refer to as sterile, dinoflagellates and slime can outcompeate everything for nutrients/habitat and take over. Part of the cure is to seed the tank with a healthy microbiome.

• Introduce pods and copepods. They graze on nuisance algae, diatoms, slimes and help reestablish ecological balance.

• Use live sand such as TBS Ultra Live Sand, which imports the biome of the ocean directly into the tank. Sand or rubble from a healthy friend’s tank can also work. The goal is to introduce predators and competitors to the dinos or slimes from sources where we can be reasonably confident they have been exposed to dinos but have found a way to remain in balance with them.

• The sump is a great place to add seeded material because it circulates microfauna through the whole system.

Step 4 — Control light and scale PAR gradually

Light is one of the biggest drivers of nuisance outbreaks. Dinoflagellates are photosynthetic organisms whose growth is largely limited by the number of photons they receive.

This is one reason LPS tanks with confirmed PAR in the 50–150 range tend to experience substantially fewer challenges with dinos. In contrast, SPS tanks running PAR in the 200–350 range are often much more susceptible, particularly in the early months.

This also applies to tanks where PAR has been tuned “by eye,” which often ends up being significantly higher than anticipated.

Overlighting a newly seeded or recovering tank will only feed the problem. Follow a blackout and slow ramp protocol. This is one of the most important steps. Simply adding new sources of microbiome will not help if you do not first set the existing dino population back through light control.

1. Blackout the tank for one full week after adding pods and live sand. If a full blackout is impossible, reduce lighting to the lowest level you can for multiple weeks. How long is based on bad your problem is and how it reacts to the light. Black out is 20x as effective as reducing light.

2. After the blackout or low-light period, scale your PAR up to your target slowly. Don’t guess at PAR levels. Use an PAR meter or watt meter to indentify the PAR. Overlighting is a common reason dinos come back with a vengeance.

3. Suggested ramp timelines: for LPS-dominated setups aim to reach target PAR over about three weeks; for SPS-heavy systems plan for around six weeks of careful ramping.

If the slimy mats disappear overnight and return during the day, that is a classic sign that a UV sterilizer might be the right tool. A good hang-on or inline UV unit can reduce free-swimming dinos and help break the cycle.

Why this works

Dinoflagellates and other nuisance organisms often thrive when the tank lacks competition from beneficial microfauna and when light fuels rapid growth. Seeding the tank restores natural grazers, the blackout starves photosynthetic nuisances, and careful PAR control prevents relapses. Together these steps remove the conditions dinos need to dominate.

Step 5 — If that doesn’t work Consider UV Sterlizers

There are two good signs that a UV sterilizer might be the next logical move.

• If the slimy mats largly disappear overnight and return during the day, that is a classic sign that the dinos are a pelagic water swimming type where a UV sterilizer can be a miracle tool.

• if the slimy mats become filled with bubbles during the day and form drippy tip slime that floats towards the surface that is a classic sign that the dinos are a pelagic water swimming type where a UV sterilizer can be a miracle tool.

In those cases a good UV unit can reduce free-swimming dinos and help break the cycle. Combined with manual removal the problem is often gone in days and stays gone as long as the UV is turned on.

The best implementation of UV is a inline option plumbed between your return pump and tank. This will stralize near all of your tanks water every hour

Just as effective is a hang on UV which will also cyclye near all of your water every hour. it is pulling from the tank, sterlizing and going directly back to the tank. Only downside is they are not attravtive and you have a pump dangling in the tank. However thats a million times more desireable than a tank full of slime.

Much less effective is a UV which reciriculates water from within the sump. The reseson it is less effective is because it only cycles a portion of whats in the sump and sometimes will not process enough of the tanks water an hour to be effective. if it is is the only option do it anyways.

Step 6 — If that doesn’t work…

You are likely in the 20% of cases where a more aggressive solution is required. There are two resources we strongly suggest using.

• Mack's reef...Dinoflagellates support group! This is a group of people who’s sole focus is solving these types of issues for reefers like you. Give them a shot, it will be helpfull.

• SR Podcast 23 ways to beat dinos! RT and Ryan explore all of the most common methods of solving dinos, causes, cures, and nothing burgers we should avoid.

• Serious Reefs Biome Cycle This is the ounce of prevention. Sometimes a reboot is in order and this is how we suggest doing it next time.

Tools and supplies you'll want

• Live sand or seeded sand (TBS Ultra Live Sand or similar)

• Pods/copepods culture

• Live rock or rubble from a healthy source

• PAR meter — the best tool to avoid overlighting

• If no PAR meter available, a cheap watt meter can be used to estimate intensity; it is far better than guessing

• Optional: UV sterilizer if slimes dissipate at night and return during the day

Frequently asked questions

How long until I should see improvement after seeding and blackout?

You should see signs of improvement within days to weeks after a proper blackout and adding pods. Full recovery and stable coral growth may take three to six weeks depending on whether you target LPS or SPS lighting levels.

Will chemical treatments alone get rid of dinoflagellates in reef tank?

Chemical treatments can reduce symptoms temporarily, but without addressing a sterile microbiome and improper lighting they rarely provide a long-term cure. Combine treatments with seeding and light control for lasting results.

Do I need an expensive PAR meter to recover my tank?

A PAR meter is the most accurate way to avoid overlighting, but if you do not have one a $30 watt meter to estimate intensity is better than guessing. Accurate light control is critical to stopping relapses. There are much more affordable ($129) par meters. They do require a correction factor, watch this video.

When should I use a UV sterilizer?

If your slime disappears overnight and returns each day, that pattern indicates free-swimming stages. A properly sized UV sterilizer can reduce those populations and aid recovery.

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Full disclaimer here The gist of it. Content is based on personal experience, not professional advice. Do your research and reef responsibly. Serious Reefs should not be your sole source of information on any topic. By watching, you agree that Serious Reefs and its creators aren’t liable for how you use this info. Please don’t utilize our information if you are not ok with this. Serious Reefs has no sponsors, doesn’t accept product or payment for reviews. We do use affiliate links that earn a small commission to support our work.

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