Where did our nitrates go?!

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ariellemermaid

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We have a 20g, for all intents and purposes, fully fledged nano reef 1 year old. It’s actually our coral and invert QT but lots of LR, sand, and some corals we’ve planted. We’ll give the crabs a little nori, a few pellets individually, and sometimes some coral food but no crazy feeding going on.

Despite this, for over a year now, we’ve battled nitrates with weekly 25-50% water changes. Nitrates typically didn’t really get any lower than 10, and usually pushing 25 before a water change. Despite this, corals flourish in this tank and all has been well.

Now to the point: due to life, it’s been between 2-3 weeks since the last water change. I figured the nitrates would be >25 and planned on a large water change and sand cleaning. To my shock they’re between 0-2 on salifert and not registering on my API! In the entire history of this tank I’ve never seen nitrates at that level. The phosphate test we have isn’t great but also looks pretty much zero. So what the heck happened?!

Aquarium details: bursting with corals at the moment as it’s taken longer than expected to get a new floor installed and set up our XXL 750. Conch’s, snails, crabs, pep shrimp, starfish. No skimmer, just a Tidal 75 HOB filter I clean every 1-2 months at most. Parameters I keep alk >8, Ca shoot for 430, and Mg I’ve never had to add; monitored by Apex and a doser. No hair algae but we did pick up some ulva that’s been a little invasive. By that I mean that little leaves of this thing have been popping up on the back wall and one snail shell, nothing seems to want to eat it. But we’re just talking about a countable number of 1/4-1/2” leaves on the back, nothing that should be able to consume so much nitrate (I think).

Could the decreased water changes and not cleaning the sand for longer than ever before have allowed anaerobic bacteria to flourish? Could it be the small amount of ulva? I’m a little scared at the moment to change anything in the tank (clean the filter, sift the sand, scrape the ulva off the back wall). I went ahead and did a 25% WC anyway but didn’t clean the sand. Just not sure how we should move forward with tank maintenance at the moment since the tank seems to be thriving with the less we do to it. Previously from a coral growth standpoint and now from a nutrient management perspective.
 
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ariellemermaid

ariellemermaid

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Your good nutrifying bacteria all over your LR is consuming it.

But I think NO3 numbers are misleading unless your tank is full of Acros.

I believe healthy tank can and do very well btwn 5 to 20 ppm.
Good point about nitrates. This tank has thrived despite many sources suggesting <5 is ideal. Or that you have to have a skimmer/sump or that an HOB filter is wrong. Despite being a QT, it’s our most thriving tank to date. Only problem we’ve had is moving the corals to our DT which has killed or almost killed several without a clear answer. Definitely not full of acros, just 3 or 4 small acro frags that are doing between great and questionable. Otherwise various SPS, LPS and softies (out of control).

Sounds like we have one vote for bacteria. Just can’t believe it took an entire year to get here!

My education thus far however is that it takes anaerobic bacteria in areas of very low flow to make the NO3 to gas NO conversion. But it sounds like you’re thinking low flow in portions of the rock are more likely?
 

Nano sapiens

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One can certainly go down the rabbit hole when trying to figure out exactly how nitrate is being utilized (or not) in a reef aquarium as there are multiple pathways.

Couple thoughts:

1. Do you clean the sand during each weekly WC? If so, you may be limiting the anoxic/anaerobic bacteria responsible for denitrification by keeping the sand bed a bit too aerobic.

2. If ammonia production decreases (less feeding, for example), there should be correspondingly less nitrate being produced by the anoxic/anaerobic bacteria. For the last few weeks without WCs, have you also added less organic material to the system?

3. Have you checked the nitrate level in you water change water? With a 25-50% WC you might have been adding some nitrate weekly to the system which kept the level up.

My 12g system (no mech or chem filtration) used to naturally run low at 0.5 - 1 ppm NO3 for 10 years until I removed a decent sized LR full or Rics. Now, it sits at between 5-10 ppm depending on how much I feed. I really don't see much difference between the low and higher levels, but I would say that having some constant measurable NO3 is beneficial.
 
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CanuckReefer

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Good point about nitrates. This tank has thrived despite many sources suggesting <5 is ideal. Or that you have to have a skimmer/sump or that an HOB filter is wrong. Despite being a QT, it’s our most thriving tank to date. Only problem we’ve had is moving the corals to our DT which has killed or almost killed several without a clear answer. Definitely not full of acros, just 3 or 4 small acro frags that are doing between great and questionable. Otherwise various SPS, LPS and softies (out of control).

Sounds like we have one vote for bacteria. Just can’t believe it took an entire year to get here!

My education thus far however is that it takes anaerobic bacteria in areas of very low flow to make the NO3 to gas NO conversion. But it sounds like you’re thinking low flow in portions of the rock are more likely?
You mention your 'softies out of control' IMO they are gobbling up those Nitrates.... not a bad thing really....mine do just that....also the good bacteria in effective live rock as Zoa mentions....
 
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CanuckReefer

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One can certainly go down the rabbit hole when trying to figure out exactly how nitrate is being utilized (or not) in a reef aquarium as there are multiple pathways.

Couple thoughts:

1. Do you clean the sand during each weekly WC? If so, you may be limiting the anoxic/anaerobic bacteria responsible for denitrification by keeping the sand bed a bit too aerobic.

2. If ammonia production decreases (less feeding, for example), there should be correspondingly less nitrate being produced by the anoxic/anaerobic bacteria. For the last few weeks without WCs, have you also added less organic material to the system?

3. Have you checked the nitrate level in you water change water? With a 25-50% WC you might have been adding some nitrate weekly to the system which kept the level up.

My 12g system (no mech or chem filtration) used to naturally run low at 0.5 - 1 ppm NO3 for 10 years until I removed a decent sized LR full or Rics. Now, it sits at between 5-10 ppm depending on how much I feed. I really don't see much difference between the low and higher levels, but I would say that having some constant measurable NO3 is beneficial.
Agreed on having something measurable is good....my corals tend to explode when nitrates are around the 5 mark....then they deplete it for awhile and tend to scale back, I feed a bit more, and back they come again....its literally a month to month thing....can see it.
 

Azedenkae

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Sounds like we have one vote for bacteria. Just can’t believe it took an entire year to get here!

My education thus far however is that it takes anaerobic bacteria in areas of very low flow to make the NO3 to gas NO conversion. But it sounds like you’re thinking low flow in portions of the rock are more likely?
Yeah I am not sure about bacteria suddenly being that active. Nitrifying do not consume nitrate, that's the job of denitrifiers, but they are indeed anaerobic. It's not just about having an area be low flow - it's if it is actually anoxic, which is not easy to achieve just out of nowhere. Low flow areas of rocks will still not be depleted of oxygen enough for denitrification to really occur.

More probably like corals are consuming nitrates, especially if the corals are really starting to flourish.
 
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ariellemermaid

ariellemermaid

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One can certainly go down the rabbit hole when trying to figure out exactly how nitrate is being utilized (or not) in a reef aquarium as there are multiple pathways.

Couple thoughts:

1. Do you clean the sand during each weekly WC? If so, you may be limiting the anoxic/anaerobic bacteria responsible for denitrification by keeping the sand bed a bit too aerobic.

2. If ammonia production decreases (less feeding, for example), there should be correspondingly less nitrate being produced by the anoxic/anaerobic bacteria. For the last few weeks without WCs, have you also added less organic material to the system?

3. Have you checked the nitrate level in you water change water? With a 25-50% WC you might have been adding some nitrate weekly to the system which kept the level up.

My 12g system (no mech or chem filtration) used to naturally run low at 0.5 - 1 ppm NO3 for 10 years until I removed a decent sized LR full or Rics. Now, it sits at between 5-10 ppm depending on how much I feed. I really don't see much difference between the low and higher levels, but I would say that having some constant measurable NO3 is beneficial.
These are some of my thoughts as well.

1) In the beginning I was cleaning the whole sand bed but cut back to doing like half per change. However another change in the past several months is that with all the corals and coral racks I haven’t been able to give the sandbed a thorough cleaning in a while so I cut back to just doing like 2 spots.

2) I never knew where the nitrates were coming from in the first place. Feeding might have been a little less in the past few weeks but even at most we’re only talking about one little 1” piece of nori that gets completely consumed per day. Reef Chili coral food maybe twice a month at most. And giving the pom Poms and emeralds a tiny pellet or two.

3) Something I’ve wondered about as well. Just tested my current batch though and 0. I’m using Fritz red box and I’ve found if I leave the water heated and mixing for more than a day I get this copious brown sediment and like an oil layer on top. So I try to use it same-day for easier brute cleaning but that’s not always possible as with my current batch. Still, no nitrates though.
 
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ariellemermaid

ariellemermaid

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You mention your 'softies out of control' IMO they are gobbling up those Nitrates.... not a bad thing really....mine do just that....also the good bacteria in effective live rock as Zoa mentions....
I hadn’t thought about this. We bought a Xenia plug in the beginning. It died, but then came back to life on the back of a rock which I was happy with. Now, we have a literal Xenia forest. It’s covered the rock it started on and spread over to the next one. Also we have a cespitularia that’s grown a ton since we added it, it’s huge for the size of the tank and has started fragging itself onto nearby plugs/the rack.

I wasn’t aware softies can be good nitrate consumers. Given the amount of Xenia and the size of the cespitularia currently in the tank, that could definitely be a possibility!

My idea for the tank was to plant frags that we accumulate over time that break off from other corals. I’m not thrilled with a weed coral taking over half the tank, but I suppose if it’s going to control nutrients and reduce my frequency of water changes I can live with that. A few months back I was really close to pulling the trigger on a Tunze comline skimmer but they’re just so expensive and of questionable utility. Also thought about adding a sump. Now, things are going better than ever so I have a hard time complaining.
 

Nano sapiens

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Back in the day, some used Xenia like macro algae in a refugium and harvested regularly for nutrient control. Biggest problem with this is that a Xenia colony can crash unexpectedly. While this can happen with certain macro algae (like Caulerpa) this is unlikely with a ball of Chaetomorpha (unless nutrients get really low), so that's what's most commonly used today.
 
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ariellemermaid

ariellemermaid

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Back in the day, some used Xenia like macro algae in a refugium and harvested regularly for nutrient control. Biggest problem with this is that a Xenia colony can crash unexpectedly. While this can happen with certain macro algae (like Caulerpa) this is unlikely with a ball of Chaetomorpha (unless nutrients get really low), so that's what's most commonly used today.
Thanks for the historical perspective; it sounds like that’s probably what we have going on given the amount of it!
 
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