Low Levels or Possible Testing Error

[poqokio]

Hello everyone, I have some problems regarding Ca and Mg levels in my tank. Maybe its testing error. I kindly request your help and commends.
I bought Aquaforest Alk, Ca and Mg tests. And did some water testing yesterday and tomorrow.
--
Yesterday test results:
Kh: 4,8, Ca:400, Mg:1155
Today I did %20 water change. Also prepared a calibration liquid with 1lt RODI water + 39gr AF Reefsalt.
Test Results:
Kh: 5,9, Ca:400, Mg:1155
--
To my understanding, I have nothing that consumes mg. To make sure, I did a mg test on calibration liquid.
Test result is again 1155.
Is it possible that, AF Reefsalt has not enough mg in it in 1025 SG level? Or im making a huge mistake that im not aware yet.
Tank details:
Tank is 5 month old. But I lost all my fish in an ich-brook outbreak. Tank is currently in fallow mode, no coral added yet. (other than one zoa frag which has been given to me before cycling ends, and it never thrived until it died)
60x45x42h cm, AIO tank

 

[Randy Holmes-Farley]

I’d ignore the magnesium. It is never consumed more than 1/10th of the calcium consumption.

What calibration fluid ?

 

[Pod_01]

Just my opinion but I suspect your salinity is low, my suggestion is to mix to 1.0262 rel. density.
1.025 is on the low end and may explain the low values for calcium and Mg… Regardless the Alk is still low, at 1.025 it should be 7.3~7.7dkh.
How are you checking your salinity?

 

[rishma]

I second the salinity questions. Extremely common issue

 

[poqokio]

I’d ignore the magnesium. It is never consumed more than 1/10th of the calcium consumption.

What calibration fluid ?

Thank you and others who have commented.
I use atc refractometer. Which shows 0 for my RODI water as well.

As I wrote in first message, I prepare calibration fluid with
1 liter RODI water (measured with kitchen food scale)
39 grams of AF Reef Salt (measured again with kitchen food scale).

I know thats not a perfect calibration fluid, but I thought it should at least match with Aquaforest's 1.025 SG values for Alk, Ca and Mg. (I checked only Mg in test fluid, didnt checked others)

 

[Randy Holmes-Farley]

I know thats not a perfect calibration fluid, but I thought it should at least match with Aquaforest's 1.025 SG values for Alk, Ca and Mg. (I checked only Mg in test fluid, didnt checked others)

I generally am not a fan of standards using a salt mix since moisture in it can be variable, but it does suggest the magnesium is test error and, again, I’d ignore it.

 

[poqokio]

I think that, maybe the scale im using measures wrong? I'm using that kitchen scale from start. And I always use 390gr Reefsalt for 10L RO/DI water.

For measuring 390gr I use a 75gr glass cup, set scale to zero, than use 195gr salt twice. Maybe it goes wrong when adjusting that tare weight reduction each time, which results in inaccurate saltwater mix.

I will double check with another kitchen scale, and will update here.

 

[slingfox]

I think that, maybe the scale im using measures wrong? I'm using that kitchen scale from start. And I always use 390gr Reefsalt for 10L RO/DI water.

For measuring 390gr I use a 75gr glass cup, set scale to zero, than use 195gr salt twice. Maybe it goes wrong when adjusting that tare weight reduction each time, which results in inaccurate saltwater mix.

I will double check with another kitchen scale, and will update here.

If you are using a cheapo refractometer then there is high probability it is reading too high salinity and therefore your real salinity is too low. This is a problem that comes up commonly on this board. What tests are you using and are you using reagents that have not expired? Have you ever done an ICP test? There are lots of ways to debug this issue include by doing an ICP, getting a reliable way to measure salinity (eg, Tropic Marine Bydrometer or VeeGee Refractometer), and making calibration fluid according Randy Holmes Farley’s instructions.

 

[Randy Holmes-Farley]

I don’t think low salinity explains all of these values. Bad magnesium testing along with actual low alk would. So would low salinity and actual low alk. Or bad alk test in both cases. 4.8 dKH and 400 ppm calcium is not low salinity.

 

[poqokio]

I made a kitchen salt calibration fluid details explained bellow:
(derived from Randy's recipe, I might make some mistake)

Used the same kitchen scale, I weight 18gr of Iodized Table Salt.
Then with the same scale, I measure 482gr RO/DI water.
Which would be 3,6 percent Sodium Chlorine to my math.

I use that solution to my refractometer, waited 30 seconds and it was beyond 1.025. I calibrated that into 1.025.
Then, I check my display tanks salinity again. The result was 1.022-1.023.

It was salinity measurement error after all.

Question 1: Should I recalibrate using with a larger calibration solution to reach 3,65 percent Sodium Chlorine solution?
Question 2: Should I re-test this measurement with another kitchen scale, just to be sure?

Thanks for all help.

 

[rishma]

(derived from Randy's recipe, I might make some mistake)

Used the same kitchen scale, I weight 18gr of Iodized Table Salt.
Then with the same scale, I measure 482gr RO/DI water.
Which would be 3,6 percent Sodium Chlorine to my math.

I use that solution to my refractometer, waited 30 seconds and it was beyond 1.025. I calibrated that into 1.025.
Then, I check my display tanks salinity again. The result was 1.022-1.023.

It was salinity measurement error after all.

Question 1: Should I recalibrate using with a larger calibration solution to reach 3,65 percent Sodium Chlorine solution?
Question 2: Should I re-test this measurement with another kitchen scale, just to be sure?

Thanks for all help.

When I recently made calibration solutions I did the following to make it more accurate.

I added 10g to the scale and tare. Scales are less accurate for small amounts when measuring from 0.0.

I made 2 solutions back to back they were within 0.2% of each other so I decided they were good. I mixed the two as my final solution.

I’d suggest floating the calibration solution in tank to get to same temp. I know it’s ATC, but having same temp removes one variable.

 

[Randy Holmes-Farley]

I made a kitchen salt calibration fluid details explained bellow:
(derived from Randy's recipe, I might make some mistake)

Used the same kitchen scale, I weight 18gr of Iodized Table Salt.
Then with the same scale, I measure 482gr RO/DI water.
Which would be 3,6 percent Sodium Chlorine to my math.

I use that solution to my refractometer, waited 30 seconds and it was beyond 1.025. I calibrated that into 1.025.
Then, I check my display tanks salinity again. The result was 1.022-1.023.

It was salinity measurement error after all.

Question 1: Should I recalibrate using with a larger calibration solution to reach 3,65 percent Sodium Chlorine solution?
Question 2: Should I re-test this measurement with another kitchen scale, just to be sure?

Thanks for all help.

That difference does not explain the low alk, but raising the salinity and the alk is a fine plan.

 

[rishma]

That difference does not explain the low alk, but raising the salinity and the alk is a fine plan.

I looked up the salt and it’s expected to be 7.7-8.3 dKH so definitely way off on alkalinity. Alk tests are usually the ones I rely on, they are rarely bad kits. I don’t have any other ideas.

 

[poqokio]

I prepare another calibration fluid. This time double scaling with another kitchen scale, just to increase precision.

I used 73 gr table salt with 1927 gr RO/DI water for preparing %3.65 solution. And then calibrated my refractometer for 1.026-35 ppt mark.

Then check my display tank salinity, which came around 1.023 SG.
I also checked my test fluid (which was prepared with 1L RO/DI + 39gr AF Reef Salt, waiting in a plastic bottle),
It was also around 1.023 SG.

I checked test fluids Alk and Ca (Couldnt test mg, because unfortunately I mistakenly left MG Reagent-D open, and its spilled all over its box. The test is no longer usable.)
Alk Result:
Ca Result: 340
Alk Result: 5.9

There must still be a problem.
In 1.022-1.023 range I should have Alk on 7.0-7.3, and Ca on 370-380 according to Aquaforest website. Either my refractometer is still out of calibration, or I'm making a testing mistake.
How can I know where im doing wrong, other than ICP test?

Also another question: I'm considering only soft corals and few LPS (1-2 hammer, 1 duncan, maybe 1 torch), Should I buy Mg test again, or I can go with only Alk,Ca? (I wont dose seperate additives, I have DIY baked baking soda for Alk, also Aquaforest Component 3-in-1 500ml)

 

[rishma]

I prepare another calibration fluid. This time double scaling with another kitchen scale, just to increase precision.

I used 73 gr table salt with 1927 gr RO/DI water for preparing %3.65 solution. And then calibrated my refractometer for 1.026-35 ppt mark.

Then check my display tank salinity, which came around 1.023 SG.
I also checked my test fluid (which was prepared with 1L RO/DI + 39gr AF Reef Salt, waiting in a plastic bottle),
It was also around 1.023 SG.

I checked test fluids Alk and Ca (Couldnt test mg, because unfortunately I mistakenly left MG Reagent-D open, and its spilled all over its box. The test is no longer usable.)
Alk Result:
Ca Result: 340
Alk Result: 5.9

There must still be a problem.
In 1.022-1.023 range I should have Alk on 7.0-7.3, and Ca on 370-380 according to Aquaforest website. Either my refractometer is still out of calibration, or I'm making a testing mistake.
How can I know where im doing wrong, other than ICP test?

Also another question: I'm considering only soft corals and few LPS (1-2 hammer, 1 duncan, maybe 1 torch), Should I buy Mg test again, or I can go with only Alk,Ca? (I wont dose seperate additives, I have DIY baked baking soda for Alk, also Aquaforest Component 3-in-1 500ml)

Magnesium is never worth testing at home IMO. Highly unreliable kits and it changes so slowly in a reef that it’s not worth worrying about. You can just dose it in proportion to your alk and Ca doses when you get to that point. Spilling your reagent saved you from a lot of frustration.

 

[Randy Holmes-Farley]

I agree about skipping a new mag test purchase.

 

[poqokio]

Thank you all for your responses.

I made another fresh saltwater batch,
This time with 5L RO/DI water and 195 gr AF Reef Salt, heated and mixed for at least 30 mins.
Than tested with refractometer. 1.024 SG and
Tested with Aquaforest Testpro Allakinity test: Kh: 6,4.
(I tested again with Sera Kh test kit, which turned yellow in 6th drop, means KH:6)
According to Aquaforest Reefsalt chart; It should be close to 7.3.

Could it be about my RO/DI water is not pure enough? The RO/DI unit is 5 months old.
Note: In my region, the tap water is relatively clean,
TDS is 20-30 without RO, 3-5 with post-carbon filter, and "0" with my RO/DI
(According to my cheap digital TDS meter).

Or maybe my ATC Refractometer is not quality enough?

Maybe the easy solution is add more salt, until I see somewhere around 7Kh, but too elevated salinity would case much larger problems and I want to be sure.

 

[slingfox]

Thank you all for your responses.

I made another fresh saltwater batch,
This time with 5L RO/DI water and 195 gr AF Reef Salt, heated and mixed for at least 30 mins.
Than tested with refractometer. 1.024 SG and
Tested with Aquaforest Testpro Allakinity test: Kh: 6,4.
(I tested again with Sera Kh test kit, which turned yellow in 6th drop, means KH:6)
According to Aquaforest Reefsalt chart; It should be close to 7.3.

Could it be about my RO/DI water is not pure enough? The RO/DI unit is 5 months old.
Note: In my region, the tap water is relatively clean,
TDS is 20-30 without RO, 3-5 with post-carbon filter, and "0" with my RO/DI
(According to my cheap digital TDS meter).

Or maybe my ATC Refractometer is not quality enough?

Maybe the easy solution is add more salt, until I see somewhere around 7Kh, but too elevated salinity would case much larger problems and I want to be sure.

Salinity testing is not the area you want to skimp on. Get some reliable way to meausure: Specifically a Tropic Marine hydrometer or VeeGee Refractometer. It is possible a cheap refractometer can work but you then potentially have to recalibrate every single time you test. To me that is too annoying.

If I were you I would just bring salinity up to 1.026sg and figure out how to make sure the salinity and all testing is correct and then bring up alk via dosing if you want to hit a target range.

If I were you I would pick up a different Alk test kit and compare with what you are currently using.

 

[poqokio]

I made two another tests:

Ca test on new 5L 1.026 saltwater. Ca:435-440
(Which is very close to AF 35ppt levels)

pH test on my RO/DI water. pH: 4.5-5 ish.

-

Does it explain the low kh levels im having? If so, I can rely on my refractometer and ca levels, and only dose baked b.soda for adjusting kh.
Thanks in advance

 

[ReneReef]

I’d suggest floating the calibration solution in tank to get to same temp. I know it’s ATC, but having same temp removes one variable.

FYI, the ATC has nothing to do with the sample temperature. It corrects for ambient temperature (the temperature the refractometer takes).

The one or two drops of sample instantly take on the temp of the refractometer.