Why aren't nitrates rising?

[dnprall]

I have a 43 gallon tank (9 gallon sump). Corals, shrimps, snails, and fish.

I had "fallen off the wagon" with water changes for quite some time. I finally got my act together and bought a Brute waste bin and starting making bulk saltwater. My corals certainly started looking better after the first couple of water changes.

I'm changing 2.5 gallons once a week.

Last year, I was having nitrates as high as 45 so I started carbon dosing with vodka. I was able to dial this so the nitrates were around 2-3. I was using 6 mL of vodka a day.

When I started doing water changes again, I started testing again. My nitrates were 0. In August 2025, I decreased the vodka to 4 mL a day. Then I dropped it to 2 mL a day in late October 2025 and then stopped it completely on 11/9/25.

I tested today and nitrates were 0 again.

Everybody in the tank appears happy. I dose All-for-reef at 16 mL a day (spread out hourly over 24 hours) and that's it. I'm using Tropic Marin Pro-Reef Salt. I have an auto feeder that uses "Reef Jerky" 3 times a day. Will occasionally put in a frozen shrimp cube.

Remaining parameters for 11/15/25: Phos 0.06, mag 1440, alk 9.3, calcium 458, pH 8.3.

The questions:
1) Is there a time frame that I should expect the nitrate to rise after stopping carbon dosing?

2) I know that overfeeding can increase nitrates. I think I'm feeding plenty. If there is not a time frame expected for nitrate to rise, should I start dosing a little NeoNitro? I understand that changes in tank biology can take a time (i.e. the bacteria that was using the carbon dosing may take time to decrease to allow nitrates to increase or maybe they won't).


Thoughts? Need any more information?

 

[exnisstech]

Could always dose some ammonium. Its what I do when I see zero in my SPS tank.

DIY Ammonia Dosing Chart

Introduction: Many reef tanks have an incredible nitrate demand, and despite the additional fish and coral food, still struggle to make an impact on the nitrate level. This can subject corals, anemones, coralline, macro/microalgae, and clams to nutrient starvation. Any photosynthetic organism...

www.reef2reef.com

 

[dnprall]

Could always dose some ammonium. Its what I do when I see zero in my SPS tank.

DIY Ammonia Dosing Chart

Introduction: Many reef tanks have an incredible nitrate demand, and despite the additional fish and coral food, still struggle to make an impact on the nitrate level. This can subject corals, anemones, coralline, macro/microalgae, and clams to nutrient starvation. Any photosynthetic organism...

www.reef2reef.com

Thanks :)

Do you do ammonium bicarbonate? If so, what kind of container have you found to keep it air tight?

You say you dose ammonium when you see zero in your SPS tank. Does the mean you don't always have it dosing to try to find a steady state? Ideally I'd put this on my dosing machine so I don't have to remember daily.

 

[exnisstech]

I do dose ammonium bicarb. I haven't bothered to try and calculate a steady dose that I could add daily. I'm sure that would be best and recommended but suck st math and I'm lazy and don't feel like setting up another doser so I just dose it manually. I test every Sunday and if I see 0 I will dose 10ml a day untill I see 2-3 ppm then stop and repeat as needed. Maybe one of these days I'll set it up as is should be but for now coral don't seem to mind the way I'm doing it so I'm just rolling along.

EDIT: Forum isn't allowing me to post images today but I have a recent tank shot in post #7 below if you want to take a look.

THEN AND NOW! Post a build pic with start date for your REEF and a current FTS shot!

My reef got wet on November 2021 and is now 4 years running…

www.reef2reef.com

 

[Randy Holmes-Farley Verified Community Expert]

Thanks :)

Do you do ammonium bicarbonate? If so, what kind of container have you found to keep it air tight?

You say you dose ammonium when you see zero in your SPS tank. Does the mean you don't always have it dosing to try to find a steady state? Ideally I'd put this on my dosing machine so I don't have to remember daily.

I do. I use a plastic Kefir bottle with a tubing hole drilled in the lid.

I dose it every day on a timer. My nitrate falls if I do not.

 

[dnprall]

I do. I use a plastic Kefir bottle with a tubing hole drilled in the lid.

I dose it every day on a timer. My nitrate falls if I do not.

Kefir bottle :) Love it. So just find a food safe plastic bottle.

Would you be willing to share where you source your ammonium bicarbonate?

Do you dose it all at once or throughout the day?

 

[JonasRoman]

As far as I understand All in one contains organic Calcium salt, Calcum Formate, meaning I think you still have organics dosing that can facilitate the denitrifikation of No3 to N2. I would never dream of dosing such all in one substances, as i want to control my addition of organics myself.
Concernin dosing nitrate, I would not do, as nitrate is just a secondary parameters telling you probably have lack of N in the system, but as N is primary for the corals (organics) or for the zooxanthelle (inorganic) I would does N in those forms that the inhabitants uses it,, so maybe urea/ammonium, or just organic particular coral food.

Jonas

 

[Randy Holmes-Farley Verified Community Expert]

Kefir bottle :) Love it. So just find a food safe plastic bottle.

Would you be willing to share where you source your ammonium bicarbonate?

Do you dose it all at once or throughout the day?

Sure. I use this from Amazon:

https://a.co/d/506ECxC

 

[Turnage]

Feed your fish more. Turn your tank into an all-you-can-eat buffet for your fish.

 

[dnprall]

Feed your fish more. Turn your tank into an all-you-can-eat buffet for your fish.

You know I was thinking about that too. I could add two more feeding sessions for the Reef Jerky and see how it goes.

 

[Turnage]

Turn off any skimmers also

 

[JonasRoman]

Turn off any skimmers also

I disagree, as the skimmers second (or even primary) job is to exchange Co2 and O2.

 

[mcarroll]

Last year, I was having nitrates as high as 45 so I started carbon dosing with vodka. I was able to dial this so the nitrates were around 2-3. I was using 6 mL of vodka a day.

When I started doing water changes again, I started testing again. My nitrates were 0. In August 2025, I decreased the vodka to 4 mL a day. Then I dropped it to 2 mL a day in late October 2025 and then stopped it completely on 11/9/25.

Things seems like they have been/still are out of balance.

How are you filtering and maintaining this tank?

I would avoid carbon dosing in most situations.

Also, how are you testing NO3 and PO4?

 

[Turnage]

I disagree, as the skimmers second (or even primary) job is to exchange Co2 and O2.

Agree they are important roll but it would be temporary to get nitrates back up. I have an air pump with an air stone for emergency situations that can be used.

 

[Randy Holmes-Farley Verified Community Expert]

I doubt that turning a skimmer off will have a quick impact on nitrate.

 

[Turnage]

I doubt that turning a skimmer off will have a quick impact on nitrate.

Never said it was a quick impact on nitrates. If you want a quick impact then you dose.

That being said as we all know, nothing good ever happens when it comes to going quick in this hobby.

 

[Randy Holmes-Farley Verified Community Expert]

I was responding to the stated "temporary" nature of the plan. IMO, it would be a long temporary, if it ever achieved raising nitrate, and I do not recommend turning off skimmers. :)

 

[dnprall]

Things seems like they have been/still are out of balance.

How are you filtering and maintaining this tank?

I would avoid carbon dosing in most situations.

Also, how are you testing NO3 and PO4?

Red Sea ReefMat and Skimmer

Hanna

 

[Luminous74]

Vodka gets metabolized within just a few hours. I’d say the biology in the tank adapts to that very quickly once you stop dosing. After that, everything shifts toward the limiting factor — and in your case I’d guess that’s nitrogen, meaning low or missing nitrate.

You can try increasing feeding a bit to see if it helps and whether nitrate starts to rise. But overfeeding for no reason doesn’t make sense either. As support, you can add nitrogen in the form of ammonium. Dose it slowly, similar to how you’d increase vodka. Once nitrate becomes measurable, you’ve reached a balance.

By the way, the amount of carbon added through AFR is negligible and doesn’t really matter in practice.