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Restarted tank, low nutrients, cyano.

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Hi Guys, 

After life happened I put my tank (25 gallon) on cruise control, sold off my delicate corals and housed my other with a fellow reefer. I have 2 clowns, a royal gramma and a pink streaked wrasse. 

Last week I restarted my tank, because of course cruise control turned into neglect. 

Scrubbed all the algae, bit by bit turned over the sand and did 3 40% waterchances in course of a week. Put in a testercoral which is doing great. 

Since starting I tested nitrates and fosfates twice and both read zero. (other parameters are not that important since 100% of the system is new water).

Because of this reading I believe I have some green cyano. It's also very easy to blow of the rock.
I feed a quarter cube of frozen food twice a day, enriched with vitamins.

Now IMO my options are: 

1. Do nothing because the corals that are in the tank are doing great and let the tank get into itself again.

2. Adress the low nutrients by either dosing p04 and nitrate directly, turning off the skimmer or feeding more. 


Already feeding half a cube and some flakes a day with 4 fish and 5 corals, adding more doesn't feel constructive.

Turning of the skimmer may affect ph and oxygen in the water.

I tend towards the dosing part myself. What do you guys think? 



Foto 03-05-2021 21 29 08.jpg

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Corals are not going to like 0 nutrients. The problem is adding nitrate or phosphate, especially phosphate might cause crazy algae growth in a young tank. That's the catch 22 of young tanks.


Sodium nitrate, food grade can be found on Amazon for cheap. Wont tank much on a 25. Maybe 1/4 teaspoon. Stump remover also works because its potassium nitrate.


Reef roids will quickly spike phosphate. 



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I caution people trying to raise inorganic nutrient levels by overfeeding.  This causes excess organics (including DOM, DOC, POC) which can encourage cyanobacteria and other problems.


Which test kits are you using?  Some kits (like the API Phosphate kit which doesn't detect phosphate below 0.25ppm) aren't high resolution kits.


Also, testing while you are experiencing a bloom might not reflect the nutrient import, as the bloom will consume the available inorganic nutrients (causing test kits to read low to undetectable levels).  As blasterman stated, dosing (while a cleaner method to import nutrients) might cause problems of is own.


You've identified the bloom as cyano (which might be correct); however, you might also be dealing with diatoms or even dinos.  Cyano is pretty common, so I assume that's what you're dealing with.  Cyano is often due to excess organics (caused by lack of maintenance, inadequate filtration or flow, and/or overfeeding).

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When my nutrients get too low I get green cyano and when they get too high I get the red crap. 

I personally never dosed anything and the nutrients eventually balanced on their own. I did however keep up with stirring out debris and removing if with floss/sock/skimmer. 

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Looks like cyano to me. Still preferable to dinos. Oh sure...every time I get cyano its the common red variety, but you get the less common green 🙂


I've never quite nailed the cause of cyano although the buggers seem to hit young tanks with unstable nutrients.


All things considered having a nitrate level stable around 10'ish really seems to help these problems in young tanks. New tank owners typucally struggle with excessive nitrate but it sounds like this is a restart which may make for some odd nutrient consumption.

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