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Nutrition during cycling


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Nov 23, 2019
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Hi all!
Im just cycling a new tank with complete dry rock.
I had no lights on for the first 3 month and threw a shrimp into the tank and added some bacteria. The bacteria broke down the shrimp and i had some nutrients in the tank all the time.
After 3 months ive added some fish and switched the lights on. 2 weeks later ive had some sign of coral alge and added some corals. They did fine. At the same time, my nutrients vanished. No3 and po4 went straight to zero and some cyano and brown algae startet to show up.
I feel that theres no way in getting some nutrients into the tank.
The tank is about 130 gallons. 18 fish inside, i feed frozen food twice a day and some pellets over the day. Still nothing detectable even if turn my skimmer off for a few days. When i dose some po4 to raise the level in the tank to 0.05 and measure it 20 minutes later its about 0.0 again. No matter how much i dose (Ive checked my tests, everything is fine). The only feeling i get is that if i dose more, ill get more cyano and brown algae. But if i keep it at 0.0 the corals arent really happy with that. In a lot of forums and clips about cycling a tank everybody talks about elevated nutrients, seems like nobody else have this issue with nutrients disappearing?
If got a good 10 years exp in reefing, so dont get me wrong, but im starting to doubt myself, because this never was an issue in my former tanks, so ive got to ask some questions.
Is it common, that new tanks suck up all the nutrients? (Even after 5 months cycling now)
What to do? Let the nutrients vanish and hope that those slimy films will die off along with the first corals?
Or still try to dose some nutrients every day? Few people told me in the past, that if you are cycling a reeftank, 0.0 at the nutrients is a no go, because even the bacteria needs something to feed on. Ive already turned the skimmer off and reduced the lighting period to 8 hrs. After good 5 months, there is still nothing to detect beside some algae and cyano.

Thanks for your thoughts on this!


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May 3, 2018
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Hey Sleepwalker, Welcome to R2R!!

I had this same issue in my first tank!! Do you have a lot of Green Hair Algae? I ask because if you do I assume they are the ones eating up the nutrients as they can chew up a lot!! What is your Clean up crew? Do you have LOTS of CUC to get started eating up that Green Hair Algae? Once you get rid of whatever is draining the tank you will be amazed at how fast it can turn around. Do you run a sump? What equipment are you running down there? Picture help a ton as well!

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