A few weeks ago I walked over to my 20 gallon nano reef and noticed that I had a cyano outbreak. Red slime was everywhere. Covering most of the substrate, creeping up onto the rockwork, and starting to touch a few of my corals. Not a good look, and definitely not something I could just ignore and hope it went away on its own.
So today I want to walk you through exactly what caused this outbreak, what I tried that DIDN'T work, and what finally cleared it out in about 6 days.
What Caused It (Again)
Here's the thing... this wasn't my first time dealing with cyano in this tank. I actually fought this exact same battle about a year ago, maybe 3 or 4 months after I first set the tank up.
This time around, it came down to two things. First, life got busy, and my regular maintenance slipped. Not dramatically, just enough. Water changes got pushed back a few days here and there, and more importantly, I stopped tracking my nutrient levels as closely as I should have. The tank had been running smoothly for so long that I got a little complacent, and the time between testing my phosphates kept stretching out longer and longer. Classic mistake.
Second, and honestly the bigger issue, is that my phosphate levels have been a recurring struggle in this tank specifically. That's the root cause here, and I'll get back to that in a minute, because Chemi-Clean is NOT the actual fix for that part.
What I Tried First
Last year, when I first dealt with this, I did what most people recommend and tried the natural approaches first.
Step one was increasing flow. The theory is that cyano tends to thrive in low-flow, stagnant spots, so I bumped up my flow pumps. Then I bumped them up again. It didn't make much of a difference.
Step two was beneficial bacteria products, specifically Microbacter 7 and Microbacter Clean. The idea is that these products help beneficial bacteria out-compete the cyano for nutrients. I tried them. Didn't really help either.
Step three, and this is the one that actually told me something useful, was testing my nitrate and phosphate levels and looking at the ratio between the two. Sure enough, my phosphates were through the roof. That told me this was a longer-term nutrient issue, not something I was going to flow-and-bacteria my way out of quickly.
Why I Turned to Chemi-Clean
So last year, while I was figuring out a longer-term plan (I was hunting for a GFO reactor I could fit on the back of the nano tank), I needed something to knock the outbreak down fast before it did real damage to my corals. That's when I tried Chemi-Clean.
It worked really well. Cleared things up, and cyano stayed gone for about a year. So when this new outbreak showed up, I didn't hesitate... I went straight back to what I knew worked.
Key Point: Chemi-Clean Is Potent Stuff
I want to stress this because it matters. This is not a gentle, natural remedy. It's basically an antibiotic-type treatment, and if you don't follow the instructions carefully, you can lose fish or corals. So please, read the directions on the box thoroughly before you dose anything.
Here's what that actually looks like in practice:
Increase oxygen levels before and during treatment. You can use an airstone, or do what I did and just raise your return pump higher so it agitates the surface and pulls in extra air.
Remove any carbon from your filtration before dosing.
Measure the correct dose for your tank size. Don't eyeball it.
Fully dissolve the powder in a cup of tank water before adding it in, so it distributes evenly instead of dumping in undissolved clumps.
Watch your protein skimmer. Mine got a bit more aggressive with bubbling during treatment, and yours might too.
The Results
Here's how the timeline actually played out.
Day 1: Heavy cyano covering the substrate, creeping onto the rockwork, starting to touch corals. Not great.
Day 2 (48 hours in): I hadn't done a single water change at this point, wanted to see the product working on its own. Already a 30 to 40% reduction. That's a fast turnaround for something that had built up over weeks.
Day 6: The only thing I'd done between day 2 and day 6 was one water change. Most of the cyano was gone. Sand looked clean, rocks were clear, and there was maybe 5% left in one small spot on the sand, which disappeared a few days after that. So realistically, 95% of it cleared up in under a week.
The Real Fix Is the Root Cause
Now, here's my point with this. Chemi-Clean is a great tool for putting out the fire fast, but it doesn't fix why the fire started in the first place. For my tank, that's phosphates. Until I get that under control long-term, I'm going to keep having this fight.
Ideally, I'd love to run a refugium on this tank, but the size of the nano and the space I have behind it make that pretty impractical. So I'm actually planning a bigger tank upgrade that should give me the room to solve this properly instead of putting a band-aid on it every year. I'll talk more about that upgrade in a future video once it's underway.
In the meantime, if you're staring at a tank covered in red slime like I was, don't overthink it. Test your nitrates and phosphates first so you actually understand your root cause, try the natural methods if you have the patience, and if things are getting bad fast, know that Chemi-Clean is a legitimate option as long as you follow the instructions carefully.
If you've dealt with cyano in your own tank, I'd love to know what worked for you, drop a comment and let me know!
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