Killed a hammer by dosing Alk the wrong way...

[Randy Holmes-Farley Verified Community Expert]

Going back to the original question - how do we find the right dose when increasing the dose daily doesn't seem to make a difference?

If we assume the salinity is 33 ppt, then raising it to 35 ppt will boost the magnesium from 1177 to 1248 ppm. That solves a lot of the issue.

Are you using a calculator to determine a dose of magnesium and/or calcium?

This is a good one:

https://reef.diesyst.com/chemcalc/chem_calc3.html

 

[BeanAnimal]

Going back to the original question - how do we find the right dose when increasing the dose daily doesn't seem to make a difference?

If increasing the dose daily is not making a difference (assuming things alk/ca are somewhat in balance), then I would question the testing methodology and/or look for precipitation like hard sand or other deposits.

if it is Mag that you re speaking of, then I would simply chalk it up to testing error.

 

[jkobel]

If we assume the salinity is 33 ppt, then raising it to 35 ppt will boost the magnesium from 1177 to 1248 ppm. That solves a lot of the issue.

Are you using a calculator to determine a dose of magnesium and/or calcium?

This is a good one:

https://reef.diesyst.com/chemcalc/chem_calc3.html

Apologies, I'm not a scientist so just trying to understand. If the Hydrometer is accepted as the gold standard (and maybe im putting too much on that) and using it I just measured the water with a result of 1.0263 sg - cant we take that to understand that salinity is where it should be?

If that's the case, why raise salinity and what would I raise it to? Isn't 1.026 basically 35ppm?

I use the BRS calculator to determine make up dosing of Ca,Alk,Mg. I have tried using the calculators to find the correct daily dosage but didnt have luck. I was told at one point that the reason for that is because a calculator designed to calculate a make up dose cant be equated to the ongoing daily dosage - maybe that's incorrect.

 

[jkobel]

If increasing the dose daily is not making a difference (assuming things alk/ca are somewhat in balance), then I would question the testing methodology and/or look for precipitation like hard sand or other deposits.

if it is Mag that you re speaking of, then I would simply chalk it up to testing error.

no precipitation evidence that I can find.

RE: Mag - Isn't it more likely that its just low because I haven't added any in a few months?

My Neptune tests (which really I only use as a trend line for Mag) were actually basically exactly the same as the ICP test.

Can you guys help me understand why we are told to basically not test for Mag because the tests are so unreliable but - so much focus here is on the Mag being low? If advice is to not really test for it (and therefore we would really not even have a measurement) why are we so focused on it?

Again, not being flip - honestly trying to understand how you're thinking about it because I'm clearly missing it/over/under thinking it.

 

[Randy Holmes-Farley Verified Community Expert]

Apologies, I'm not a scientist so just trying to understand. If the Hydrometer is accepted as the gold standard (and maybe im putting too much on that) and using it I just measured the water with a result of 1.0263 sg - cant we take that to understand that salinity is where it should be?

If that's the case, why raise salinity and what would I raise it to? Isn't 1.026 basically 35ppm?

I use the BRS calculator to determine make up dosing of Ca,Alk,Mg. I have tried using the calculators to find the correct daily dosage but didnt have luck. I was told at one point that the reason for that is because a calculator designed to calculate a make up dose cant be equated to the ongoing daily dosage - maybe that's incorrect.

Oceanographers do not use hydrometers. They use conductivity, and in fact the modern salinity scale is based on conductivity. Reefers like hydrometers because they do not change calibration, but that does not mean they are accurate. Have you ever checked to see if it is?

That said, I do not know which is accurate between what you did and what Fauna did. Fauna likely used conductivity because they actually give a conductivity value, but they may have done it incorrectly, or may have merely calculated it from some other type of measurement.

FWIW, I measure salinity by conductivity.

 

[Randy Holmes-Farley Verified Community Expert]

no precipitation evidence that I can find.

RE: Mag - Isn't it more likely that its just low because I haven't added any in a few months?

My Neptune tests (which really I only use as a trend line for Mag) were actually basically exactly the same as the ICP test.

Can you guys help me understand why we are told to basically not test for Mag because the tests are so unreliable but - so much focus here is on the Mag being low? If advice is to not really test for it (and therefore we would really not even have a measurement) why are we so focused on it?

Again, not being flip - honestly trying to understand how you're thinking about it because I'm clearly missing it/over/under thinking it.

On the magnesium issue, I discuss it in the link below, but since both icp and your kit were low, even corrected to 35 ppt, I’d add it per a calculator. I do not measure it.

https://www.reef2reef.com/threads/just-say-no-to-magnesium-testing-rmm-is-born.1017528/

 

[jkobel]

Oceanographers do not use hydrometers. They use conductivity, and in fact the modern salinity scale is based on conductivity. Reefers like hydrometers because they do not change calibration, but that does not mean they are accurate. Have you ever checked to see if it is?

That said, I do not know which is accurate between what you did and what Fauna did. Fauna likely used conductivity because they actually give a conductivity value, but they may have done it incorrectly, or may have merely calculated it from some other type of measurement.

FWIW, I measure salinity by conductivity.

Understood, I have calibrated my probe, but it's been a few months. Interestingly, my probe is called a "conductivity probe" but the measurement it provides is in ppm which I take as "salinity". Is there a way to get the conductivity measurement in the Apex that you know of? How do you take a conductivity reading?

I have a refractometer, glass hydrometer and this conductivity probe. I have been assuming the hydrometer is accurate but with these 3 instruments, how does one determine accuracy? do I need more instruments? in the past I have been calibrating my refractometer to my hydrometer...

 

[jkobel]

On the magnesium issue, I discuss it in the link below, but since both icp and your kit were low, even corrected to 35 ppt, I’d add it per a calculator. I do not measure it.

https://www.reef2reef.com/threads/just-say-no-to-magnesium-testing-rmm-is-born.1017528/

will do, this makes sense and is what I typically do every 6 months or so when I notice its under 1200. I didn't realize that low magnesium keeps calcium low.

Thank you for this!

 

[Randy Holmes-Farley Verified Community Expert]

I have been assuming the hydrometer is accurate but with these 3 instruments, how does one determine accuracy? do I need more instruments? in the past I have been calibrating my refractometer to my hydrometer...

Make a hydrometer standard and test your hydrometer in it. All you need is a scale and some dry table salt.

Any device (such as the Apex) with a drop in probe is measuring salinity by conductivity. They do internal conversions to produce other units, such as specific gravity or salinity (ppt), which is only likely to be wrong if there are temperature corrections being misapplied (or not applied at all).

https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/

 

[BeanAnimal]

Understood, I have calibrated my probe, but it's been a few months. Interestingly, my probe is called a "conductivity probe" but the measurement it provides is in ppm which I take as "salinity". Is there a way to get the conductivity measurement in the Apex that you know of? How do you take a conductivity reading?

The probe is conductivity, but they are converting the conductivity value to a Salinity value. If they don't expose the actual conductivity value, you will have to back into it.

Conductivity, salinity, and density are related, but conversion between them is not straightforward. It relies on the seawater equation of state, which has evolved over time.

I’m not sure which algorithm Neptune uses for its conversions, but assuming that you use 35 ppt reference solution, then I assume PSS-78 (1970s) and not actually equation of state (2010 or so forward). Not a huge difference and PSS-78 may be a bit easier to compute. Easy is subjective here, both sets of equations are actually rather complex.

I don't see a need for you to convert back and forth, but I have a calculator on my site for the Tropic Marin Hydrometer. You can leverage it for your conversions if you like. It is based on TEOS-10 (equation of state of seawater) as well as a lookup table interpolation for sanity check.

https://beananimal.com/tools/tropic-marin-precision-hydrometer-correction-calculator/

 

[jkobel]

Make a hydrometer standard and test your hydrometer in it. All you need is a scale and some dry table salt.

Any device (such as the Apex) with a drop in probe is measuring salinity by conductivity. They do internal conversions to produce other units, such as specific gravity or salinity (ppt), which is only likely to be wrong if there are temperature corrections being misapplied (or not applied at all).

https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/

Ok, I just calibrated the conductivity probe using 53k solution and my Apex measured salinity has dropped from 36.4 to 32.7 which is close to the Fauna Marin ICP results of 33. Unfortunately, it's WAY off from my hydrometer so I guess making calibration fluid for that is my next step. I do use a temp probe to correct the conductivity probe with the Apex.

a couple questions related to making the calibration standard:

Is it critical that I have the water temp be the same as my tank for the measurement or can I do a conversion after the fact?

Can I use tap water as my "fresh water" or does it need to be RODI?

thx everyone

 

[jkobel]

The probe is conductivity, but they are converting the conductivity value to a Salinity value. If they don't expose the actual conductivity value, you will have to back into it.

Conductivity, salinity, and density are related, but conversion between them is not straightforward. It relies on the seawater equation of state, which has evolved over time.

I’m not sure which algorithm Neptune uses for its conversions, but assuming that you use 35 ppt reference solution, then I assume PSS-78 (1970s) and not actually equation of state (2010 or so forward). Not a huge difference and PSS-78 may be a bit easier to compute. Easy is subjective here, both sets of equations are actually rather complex.

I don't see a need for you to convert back and forth, but I have a calculator on my site for the Tropic Marin Hydrometer. You can leverage it for your conversions if you like. It is based on TEOS-10 (equation of state of seawater) as well as a lookup table interpolation for sanity check.

https://beananimal.com/tools/tropic-marin-precision-hydrometer-correction-calculator/

this converter is what I was looking for, I should have read your post before replying to Randy with my question about temperature

thanks!

Edit:
I now see that its just for TM hydrometers, I'm not sure what mine is so I will need to find that out...

 

[BeanAnimal]

this converter is what I was looking for, I should have read your post before replying to Randy with my question about temperature

thanks!

Edit:
I now see that its just for TM hydrometers, I'm not sure what mine is so I will need to find that out...

The hydrometer should have a temperature constant or reference on it. It may not have a compensation table or equation, but at the very least it should have the calibration temperature. Even if not, it not a huge deal for most and you can likely assume 25C for the reference temp.

 

[Randy Holmes-Farley Verified Community Expert]

Ok, I just calibrated the conductivity probe using 53k solution and my Apex measured salinity has dropped from 36.4 to 32.7 which is close to the Fauna Marin ICP results of 33. Unfortunately, it's WAY off from my hydrometer so I guess making calibration fluid for that is my next step. I do use a temp probe to correct the conductivity probe with the Apex.

a couple questions related to making the calibration standard:

Is it critical that I have the water temp be the same as my tank for the measurement or can I do a conversion after the fact?

Can I use tap water as my "fresh water" or does it need to be RODI?

thx everyone

Ro/di is best. No reason to not use it. Temp doesn’t matter, except it is easiest to check a hydrometer at its designed temp.

 

[Randy Holmes-Farley Verified Community Expert]

I now see that its just for TM hydrometers, I'm not sure what mine is so I will need to find that out...

That’s interesting. I don’t know of many other hobby brands of floating glass hydrometer. Be sure it is even reading in specific gravity rather than density.

 

[jkobel]

ok-

I made the standard per the document Randy sent.
I measured with my TM hydrometer and got a reading of 1.0262 @ 74.1 degrees
I put that into the calculator provided by beananimal and the calculated sg = 1.0259.
I think that's telling me that my hydrometer is .0003 off.

If that is true, and I just measured my tank water and got a result on the hydrometer of 1.0266, then after adjusting based on my calibration, my sg is 1.0263 which seems basically good - does this track or did i miss a step?

If all that is right, I dont see how my conductivity probe is saying that my salinity is 32.7 or why FM ICP was reading salinity as 33.

I've started raising my magnesium and calcium with adjustment doses since salinity seems to be right.

Going back to the initial question of how to find the right dose - what do you guys recommend? Increase by 5 ml/day until an equilibrium is reached? is that too much or too little?

In the past ,i was increasing by 5-10 ml/day and i never found an equilibrium, the tank just seemed to consume it all. My goal is to have an SPS dominant system so i really need to figure this out - I appreciate your insights.

current params

Ca - 401
Alk - 9.27
Mag - 1273

 

[Randy Holmes-Farley Verified Community Expert]

ok-

I made the standard per the document Randy sent.
I measured with my TM hydrometer and got a reading of 1.0262 @ 74.1 degrees
I put that into the calculator provided by beananimal and the calculated sg = 1.0259.
I think that's telling me that my hydrometer is .0003 off.

If that is true, and I just measured my tank water and got a result on the hydrometer of 1.0266, then after adjusting based on my calibration, my sg is 1.0263 which seems basically good - does this track or did i miss a step?

If all that is right, I dont see how my conductivity probe is saying that my salinity is 32.7 or why FM ICP was reading salinity as 33.

I've started raising my magnesium and calcium with adjustment doses since salinity seems to be right.

Going back to the initial question of how to find the right dose - what do you guys recommend? Increase by 5 ml/day until an equilibrium is reached? is that too much or too little?

In the past ,i was increasing by 5-10 ml/day and i never found an equilibrium, the tank just seemed to consume it all. My goal is to have an SPS dominant system so i really need to figure this out - I appreciate your insights.

current params

Ca - 401
Alk - 9.27
Mag - 1273

None of those seem to need raising, but if you want to, I’d use food or pharma grade calcium chloride and either magnesium chloride, or 10:1 chloride sulfate that BRS may sell.

This calculator can be used:

https://reef.diesyst.com/chemcalc/chem_calc3.html

 

[jkobel]

Thanks Randy, I'll look


just one more question -
I just noticed that somehow my sg has gone from 1.0263 yesterday to 1.0267 (measured) today. The only thing I changed was adding a corrective dose of magnesium and a corrective dose of calcium.

Would that have changed the specific gravity?