Good afternoon,
First off, I am only leaving this here as a place for new and intermediate reefers to find some information. I by no means claim to be an expert but am only providing this "trial, error and success" steps that I took to solve a major problem that I do not see discussed very much, nor covered in many articles. Largely information I had to piece together and risk testing on my own. This is largely because it doesn't seem to be a very common problem. Seeing as I almost quit the hobby myself over it, I know that there is someone else out there struggling with the same problem and/or wanting to shut their system down.
The problem:
High Nitrates and Low Phosphates. By high nitrates I mean constantly rising, off the charts nitrates with phosphates at or "near-zero". Something like 100ppm NO3 and 0.02 phosphate.
The symptoms:
Nitrates will not come down. Phosphate will not go up. You have a good skimmer thats not pulling much, youve maybetried carbon dosing, a refugium or a denitrator, you're doing large water changes (50%+) multiple times a week but the nitrate just shoots back up within a day. You've cleaned everything you can, have no visible dead spots. Zero to very small amounts of Algae Growth. Water looks clean. Corals seem to be okay but don't thrive, some die fairly quick. SPS dies at an almost 100% rate.
The cause:
In short, it could be a lack of phosphate. For me it was GFO stripping all/most PO4. But for others it could be something else that disproportionately removes more PO4 that NO3.
Things to take into consideration:
Redfield Ratio. There is a lot of information here so I urge you to look into it if you are having this problem. The basics of it are as such: 106 Carbon to 16 Nitrogen (Nitrate) to 1 Phosphate. Now there is a lot of discussion surrounding Redfield Ratio and the importance of aiming for it, however it does illustrate that organisms in the home aquaria that dispose of Nitrate do require phosphate and carbon in order to do so. If you are at 100ppm NO3 and 0.02 PO4, you are at a NO3 to PO4 ratio of 5000:1. This will undoubtably hinder NO3 reduction.
The solution:
- Disable all phosphate removal media and go back to basics. Absolutely no GFO.
- Use the redfield ratio as a loose guideline and SLOWLY rebalancing the system through phosphate dosing. Depending on how out of whack your system is, you can do this from simply feeding more "high-phosphate" foods or dosing something like Brightwell's NeoPhos. I chose NeoPhos as I didn't want decomposing extra food to exacerbate the nitrate problem since I was over 100ppm Nitrate already.
- Test Phosphates daily. I recommend getting a Hanna ULR Phosphorous Checker to save you time. Pay attention to what youre bottoming out at. For me, my readings consistently came back 0.02. Most advice will tell you this is a great number to be at, however due to the steadfastness of this number, I believe that my results were actually zero. These tests can have a margin of error.
- Dose Safe Amounts of Phosphate Daily. if you are seeing a consistent zero or near zero measurement, dose a small amount of phosphate that, per instructions, should bring you up to say .04 total ppm. Test the following day and see where you are at. If you are back down to your zero/near zero levels, this is a "good sign". Something is consuming your phosphate. Something needed it. Do that for a week and if you keep coming back to zero daily, up the dose to bring you to .08 and test daily again. Your phosphate could be going one of a few places: Absorbed by rock, consumed by bacteria or consumed by algae. You may start seeing small, decreases in your nitrates at this point. If ever you test and the level hasn't come down to your original zero/near zero reading do not dose. You do not want to over do it because it can have negative side effects on your living organisms in high amounts.
- Pay attention to the algae/cyano. If ever a meaningful amount algae begins to pop up, stop dosing phosphate and see what happens to the algae. If it grows, there is still phosphate in the water, if it dies that means that there isnt. Essentially treat the algae like a visual representation of the denitrifying bacteria who are also vying for the same PO4 and NO3.
My end experience:
When I first dosed PO4, my tank was absorbing it at an absurd rate (.08 gone in 2 hours) and I had no algae. This gradually slowed down over time (.08 in 2 days) with small amounts of Cyano. My nitrate dropped from 100+ to a consistent 50 at about the 2 month mark with medium amounts of Cyano after each dose. At this point dosing once every 2-3 days. This tanked to 10ppm about a month later with a huge cyano outbreak after one of the doses. I siphoned this out as it signified the end of the need to dose as the PO4 was being mostly absorbed by algae. My phosphates still remain in the .04 range with Nitrate at 5.
Again, this I am not an expert nor claim to be. Just sharing my experience in hopes that it might help someone like me who was really struggling for a very long time with this issue. If it helps 1 person, I'm glad I took the time to post. Please call me out if something is wrong or you have any questions.
Happy reefing and happy new year
