Cyano Bloom + Nitrite Spike — Help Needed Before System Crashes

[Blue00]

Hey everyone,
I’m reaching out for help because my system is currently going through a rough patch, and I want to avoid a full crash.
Tank is a 200L total volume about 9 month old, and things were fairly stable until recently.

Current water parameters:

• Nitrite (NO₂): 0.50 mg/L
• Nitrate (NO₃): 10 mg/L
• Phosphate (PO₄): 0 (undetectable)
• Ammonia: Not tested recently, but no clear signs of spike
• Salinity: 1.025
• Temp: 25.5–26.5°C

I've been fighting a cyano bloom for about a month now. It started on the sandbed and has now spread onto the rocks.
I'm currently dosing live phytoplankton daily to try to deal with it
Now I’m facing a nitrite spyke — 0.50 mg/L as of today — which is very alarming.
I’m preparing for a large water change (~25%) and adding bacteria (TM Nitribiotic or similar), but I’m unsure how to proceed without upsetting the biological stability even more. I stopped amino and nutrient dosing temporarily.

Questions:

• Has anyone managed to beat a cyano outbreak biologically while dealing with NO₂/NO₃ instability?
• Should I continue phytoplankton dosing, or pause it due to the nitrite spike?
• Would it help to vacuum out the cyano on rocks before it releases more toxins?
• Is this a case where I should consider a treatment like TM CyanoControl or Chemiclean as a backup?

Thanks in advance for any help

 

[Popeye_ali]

Hey everyone,
I’m reaching out for help because my system is currently going through a rough patch, and I want to avoid a full crash.
Tank is a 200L total volume about 9 month old, and things were fairly stable until recently.

Current water parameters:

• Nitrite (NO₂): 0.50 mg/L
• Nitrate (NO₃): 10 mg/L
• Phosphate (PO₄): 0 (undetectable)
• Ammonia: Not tested recently, but no clear signs of spike
• Salinity: 1.025
• Temp: 25.5–26.5°C

I've been fighting a cyano bloom for about a month now. It started on the sandbed and has now spread onto the rocks.
I'm currently dosing live phytoplankton daily to try to deal with it
Now I’m facing a nitrite spyke — 0.50 mg/L as of today — which is very alarming.
I’m preparing for a large water change (~25%) and adding bacteria (TM Nitribiotic or similar), but I’m unsure how to proceed without upsetting the biological stability even more. I stopped amino and nutrient dosing temporarily.

Questions:

• Has anyone managed to beat a cyano outbreak biologically while dealing with NO₂/NO₃ instability?
• Should I continue phytoplankton dosing, or pause it due to the nitrite spike?
• Would it help to vacuum out the cyano on rocks before it releases more toxins?
• Is this a case where I should consider a treatment like TM CyanoControl or Chemiclean as a backup?

Thanks in advance for any help

Sounds like your nitrifying bacteria have taken a hit. A nitrite reading at 9 months old strongly suggests your system’s cycle is destabilised — either from a die-off, over-cleaning, or something interfering with the biofilter.

I’d definitely hold off on Chemiclean or CyanoControl for now — using them while nitrite is present could do more harm than good. Your plan for a 25% water change and adding bacteria like TM Nitribiotic is the right move. I’d dose that daily for a few days to reseed the system and help push nitrite back to 0.

I’d also pause the phyto dosing for now. While phyto can be beneficial long-term, right now it might be fuelling instability or feeding the cyano if the system’s struggling to process organics.

Definitely siphon the cyano from the rocks — you’ll physically remove organics and limit the spread. It can release nasty stuff as it dies off, so better out than in.

Last thought: test ammonia just to rule out a full-cycle crash. If that’s showing too, the tank may be mid-cycle again. Otherwise, I’d focus on stabilising the core biology before reaching for chemical treatments.

Hope it levels out soon — sounds recoverable with the right moves.

 

[Blue00]

Sounds like your nitrifying bacteria have taken a hit. A nitrite reading at 9 months old strongly suggests your system’s cycle is destabilised — either from a die-off, over-cleaning, or something interfering with the biofilter.

I’d definitely hold off on Chemiclean or CyanoControl for now — using them while nitrite is present could do more harm than good. Your plan for a 25% water change and adding bacteria like TM Nitribiotic is the right move. I’d dose that daily for a few days to reseed the system and help push nitrite back to 0.

I’d also pause the phyto dosing for now. While phyto can be beneficial long-term, right now it might be fuelling instability or feeding the cyano if the system’s struggling to process organics.

Definitely siphon the cyano from the rocks — you’ll physically remove organics and limit the spread. It can release nasty stuff as it dies off, so better out than in.

Last thought: test ammonia just to rule out a full-cycle crash. If that’s showing too, the tank may be mid-cycle again. Otherwise, I’d focus on stabilising the core biology before reaching for chemical treatments.

Hope it levels out soon — sounds recoverable with the right moves.

thanks for the response, and yes I was pretty sure that something had happened to the nitrifying bacteria, and most likely it was totally my fault since during the water changes I was sucking out the crap that was on the sand, not realizing that on top of that stuff I was removing the good bacteria from the system.

Is 1 ml per day of TM Nitribiotic enough or too much in your opinion? also should i add reef actif on top of that?

 

[bluemon]

thanks for the response, and yes I was pretty sure that something had happened to the nitrifying bacteria, and most likely it was totally my fault since during the water changes I was sucking out the crap that was on the sand, not realizing that on top of that stuff I was removing the good bacteria from the system.

Is 1 ml per day of TM Nitribiotic enough or too much in your opinion? also should i add reef actif on top of that?

Sucking up crud from the sand would not impact your nitrifying bacteria.

They live in rocks mostly, and would be impossible to remove unless you remove rocks.

I’m betting the nitrite is a red herring for the cyano. A little bit of nitrite isn’t too unusual to be showing up ime sometimes

Really need more info:

How are your tank inhabitants looking?

Do you have a Refugium?

What are you dosing in terms of nutrients, and why did you start dosing them? Was it to fight cyano, or because they bottomed out? Which came first?

Are you dosing pytho to feed, or just to fight cyano?

I would stop dosing anything N P related, from nutrients to aminos to phyto, and see where that takes you the next few days with regular cyano removal. Then I would try to use Chemiclean if nothing improves

 

[Blue00]

Sucking up crud from the sand would not impact your nitrifying bacteria.

They live in rocks mostly, and would be impossible to remove unless you remove rocks.

I’m betting the nitrite is a red herring for the cyano. A little bit of nitrite isn’t too unusual to be showing up ime sometimes

Really need more info:

How are your tank inhabitants looking?

Do you have a Refugium?

What are you dosing in terms of nutrients, and why did you start dosing them? Was it to fight cyano, or because they bottomed out? Which came first?

Are you dosing pytho to feed, or just to fight cyano?

I would stop dosing anything N P related, from nutrients to aminos to phyto, and see where that takes you the next few days with regular cyano removal. Then I would try to use Chemiclean if nothing improves

no refugium yet.
The inhabitants seem to be in good condition, no signs of stress, neither fish nor corals. As for nutrients, I started dosing TM Amminoorganic 2 months ago 2ml daily, not to fight anything, but only to increase the growth of the corals, which happened very quickly.
as for phyto, I started adding it a couple of weeks ago since the cyano situation became unsustainable, both to fight the cyano and as a food source for the corals.

 

[Mr. Mojo Rising]

What even prompted you to test nitrite in a 9 month old tank? Did you measure ammonia also? Which tester did you use? Do you do regular weekly water changes?

 

[Blue00]

What even prompted you to test nitrite in a 9 month old tank? Did you measure ammonia also? Which tester did you use? Do you do regular weekly water changes?

so basically, i test no3 more or less every month, and this time the reading was higher than the usual so i did a full test on both no2 no3 and po4, founding that the balance is shifted, the test kits that i used was elos. For the ammonia, i currently do not have a test kit, i'll get one asap.
as for the water change i do 10% weekly

 

[Fish Fan]

I'm not sure about the Elos test kit specifically, but many hobby-level test kits are not the most accurate, and can show a small amount of ammonia and/or nitrite when the concentration is likely much lower (near zero).

I don't believe that you would randomly have nitrites in a 9 month old tank. I would bring a sample of water to your local fish store and ask them to double check your findings.

Nitrite is non-toxic in marine aquaria, so most of us don't bother to test for it, or worry about it