Crazy nutrient imbalance

[GiannisK]

I'm very confused about my corals because it seems to me they are sucking in nitrate but not phosphate. I have a 20 gallon with 3 each of softies, lps, and sps. Tank is 7 months old.

Parameters:
Temp: 78-79
Salinity: 1.026
Nitrate: 5 ppm (Salifert, today)
Phosphate: 0.18 ppm (Hanna, today)
Alkalinity: 7.6 dKH (Hanna 3 days ago)
Calcium: 420 ppm (Salifert, 7 days ago, very stable at 400 or 420)
pH: 7.8 (API, 4 days ago)
Magnesium: 1170 ppm (Salifert, today)

I tested both my nitrate and phosphate 3 days ago. Nitrate was at 5, and is now still 5. Phosphate was at 0.03 (I had brought it down from 0.25 using phosguard), and is now all the way back to 0.18. This is shocking to me, as phosphate grew from 0.22 on the 9th, to 0.24 on the 11th, to 0.25 on the 13th, then was brought to 0.03, and within 3 days is already back to 0.18. In other words, it grew by about 0.01 a day before being brought down, to now being raised by 0.06 a day. It can't be the phosguard leeching it out because as soon as I tested 0.03 I knew I overcorrected and removed it entirely.

I'm tempted to think that something might have died, like a snail...however, my nitrates haven't risen at all!

Another problem is the magnesium...until last week I had never tested magnesium before and I was shocked to see it so low. I regularly dose calcium supplements (Fluval 3-ions), which have worked very well to always keep it at 400-420. What shocks me is that this product, like many calcium supplements, is also supposed to increase magnesium. On the bottle it says 80 g/L calcium and 12 g/L magnesium. I've started dosing magnesium independently using Brightwell magnesion...my coralline growth has been skyrocketing lately, perhaps they consume a ton of magnesium?

I don't know how concerned I should be...I feed the minimum TDO pellets to my fish a day, and do a 25% water change every other week. I was gifted lots of phosguard so its not a problem for me to add some more and bring phosphates down but I don't want to keep stressing the system with changes.

If you have any advice about what might be causing my chemical imbalances or what I should do please let me know!

 

[gbroadbridge]

I'm very confused about my corals because it seems to me they are sucking in nitrate but not phosphate. I have a 20 gallon with 3 each of softies, lps, and sps. Tank is 7 months old.

Parameters:
Temp: 78-79
Salinity: 1.026
Nitrate: 5 ppm (Salifert, today)
Phosphate: 0.18 ppm (Hanna, today)
Alkalinity: 7.6 dKH (Hanna 3 days ago)
Calcium: 420 ppm (Salifert, 7 days ago, very stable at 400 or 420)
pH: 7.8 (API, 4 days ago)
Magnesium: 1170 ppm (Salifert, today)

I tested both my nitrate and phosphate 3 days ago. Nitrate was at 5, and is now still 5. Phosphate was at 0.03 (I had brought it down from 0.25 using phosguard), and is now all the way back to 0.18. This is shocking to me, as phosphate grew from 0.22 on the 9th, to 0.24 on the 11th, to 0.25 on the 13th, then was brought to 0.03, and within 3 days is already back to 0.18. In other words, it grew by about 0.01 a day before being brought down, to now being raised by 0.06 a day. It can't be the phosguard leeching it out because as soon as I tested 0.03 I knew I overcorrected and removed it entirely.

I'm tempted to think that something might have died, like a snail...however, my nitrates haven't risen at all!

Another problem is the magnesium...until last week I had never tested magnesium before and I was shocked to see it so low. I regularly dose calcium supplements (Fluval 3-ions), which have worked very well to always keep it at 400-420. What shocks me is that this product, like many calcium supplements, is also supposed to increase magnesium. On the bottle it says 80 g/L calcium and 12 g/L magnesium. I've started dosing magnesium independently using Brightwell magnesion...my coralline growth has been skyrocketing lately, perhaps they consume a ton of magnesium?

I don't know how concerned I should be...I feed the minimum TDO pellets to my fish a day, and do a 25% water change every other week. I was gifted lots of phosguard so its not a problem for me to add some more and bring phosphates down but I don't want to keep stressing the system with changes.

If you have any advice about what might be causing my chemical imbalances or what I should do please let me know!

The phosphate is likely to be unbinding from carbonate surfaces such as rocks and aragonite substrates.

It will unbind until it reaches equilibrium with the water.

When you remove phosphate from the water it will bounce back up as it unbinds from the rock.

You simply need to keep using phosphate remover until the level stabilises where you want it.

I would double check the Mg level with another test before making major adjustments as Mg is not consumed in large amounts in a typical aquarium.

 

[GiannisK]

The phosphate is likely to be unbinding from carbonate surfaces such as rocks and aragonite substrates.

It will unbind until it reaches equilibrium with the water.

When you remove phosphate from the water it will bounce back up as it unbinds from the rock.

You simply need to keep using phosphate remover until the level stabilises where you want it.

I would double check the Mg level with another test before making major adjustments as Mg is not consumed in large amounts in a typical aquarium.

Thanks for your reply! That makes sense. I’ll keep bringing it down and test carefully so it doesn’t bottom out. I’ll also order another magnesium test kit because that really does seem strange.

 

[Randy Holmes-Farley]

Thanks for your reply! That makes sense. I’ll keep bringing it down and test carefully so it doesn’t bottom out. I’ll also order another magnesium test kit because that really does seem strange.

Magnesium testing is so fraught with error that I most often do not recommend doing it at all. But if you want to do so, try the kit on some new salt water.

Just say NO to magnesium testing: RMM is born

OK, this thread has been many years in the making, and I'm posting it here since folks in the chem forum are probably already tired of all the threads relating to problematic magnesium testing. I'm going to propose a method, let's call it the Randy Magnesium Method, or RMM for short. All good...

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