Mag/Calc/Alk Testing Confusion

[Kalebos]

I am pretty confused right now and could use some input from the community. My mixed reef tank is a young 20g AIO. It is about 1 year old and has only had lps for the past 6 months. I figured at this point it would be a good idea to start monitoring my calc/mag/alk considering I have a decent amount of lps in there and intend to get a bit more. I tested my mag yesterday and was concerned because the results showed around 900ppm.

So today I mixed a fresh batch of saltwater and tested those parameters as a control. I did multiple tests of each and came away with ~925 Mag ~365 Calc ~8.4 Alk. Also, I use Instant Ocean Reef Crystals which are advertised at 455 Calc & 1345 Mag at 1.026 salinity. I mix my water to 1.025, so I expected my numbers to be a big lower, but not this low. The only number that seemed fine to me was my alkalinity reading.

Please note that I reread instructions, watched videos and did multiple tests to insure this was not an error on my part. I am wondering if Reef Crystals (or my batch) just sucks or if I have defective tests. Before I start dosing anything I want to make sure I am confident that I know what my parameters are. It is also worth noting that my tank looks absolutely gorgeous right now. Every single torch, hammer, frogspawn, acan, zoa, chalice & birds nest are vibrant/plump and have been for their entire lives in my tank.

Also, all of my test kits are Salifert.

Any input is much appreciated!

 

[rishma]

Salinity measurement errors are extremely common. Tell us how you measured salinity and how you calibrated that device.

 

[Kalebos]

Salinity measurement errors are extremely common. Tell us how you measured salinity and how you calibrated that device.

I have a refractometer that I calibrate monthly using 2 different control samples.

 

[rishma]

I have a refractometer that I calibrate monthly using 2 different control samples.

Did you make either of the calibration solutions? I’d have more trust in a diy solution but two different calibration solutions is a good start.

In general I’d disregard a home magnesium test. They are so prone to error prime as to not be very helpful.

Everything being low seems like a red flag. I think reef crystals mixes to like 9-12 dKH. Assuming all your values are right it indicates a salinity of 1.018 or 1.020.

If that isn’t right, what would explain it? I guess the potassium chloride would have to be really high to make up the salinity. Seems unlikely.

 

[Kalebos]

Did you make either of the calibration solutions? I’d have more trust in a diy solution but two different calibration solutions is a good start.

In general I’d disregard a home magnesium test. They are so prone to error prime as to not be very helpful.

Everything being low seems like a red flag. I think reef crystals mixes to like 9-12 dKH. Assuming all your values are right it indicates a salinity of 1.018 or 1.020.

If that isn’t right, what would explain it? I guess the potassium chloride would have to be really high to make up the salinity. Seems unlikely.

Interesting. I will see about getting another way to verify my salinity. The weird part of all of this though is how all measurements point to something being awry but the tank eye test passes.

 

[Fish Fan]

I would suggest taking a look at a DIY calibration solution as @rishma suggested above. Here's the link, and you just need regular Morton's table salt and a decent kitchen gram scale:

Reef Aquarium Salinity: DIY Calibration Standards

Reef Aquarium Salinity: DIY Calibration Standards By Randy Holmes-Farley One of the most important issues facing marine aquarists is providing a suitable environment for their aquaria's inhabitants. Among the important properties for a marine...

www.reef2reef.com

 

[ReneReef]

All good advice!

One important detail:
An S.G. of 1.025 does not equal a salinity of 35‰ (the ocean average around most tropical reefs). The data on the bucket assume mixing to 35‰. That would mean an S.G. of 1.0264.
So you are over 5% low from the start. However, this does not explain the entire deviation.

Yes I agree there is most likely a large error in the salinity measurement.

Bi-monthly calibration of a refractometer can be enough, but it usually isn’t. If the room temperature it is kept in changes daily, it will likely loose calibration within a week.
Also, calibrating to two points is simply NOT a thing in refractometers. You will have calibrated it to the last point you used.

 

[Randy Holmes-Farley]

I agree that ensuring the salinity is OK is the number one priority.

I also expect the magnesium value is wildly inaccurate even if the salinity is low, and I'd stop testing it at all.

 

[Kalebos]

@Randy Holmes-Farley @ReneReef @Fish Fan

So my salinity results have confused me even more. I have left my refractometer as is, I have not adjusted its calibration at all. Currently my tank reads ~32.5 PSU. The two separate "Continuum" samples I have that are advertised as 35 PSU are both reading at ~37.5 PSU right now. I went ahead and made a sample sample per Randy's guide with iodized salt and RODI water and that read ~38 PSU.

If I recalibrate per those methods, then I would need even less salt which does not add up considering my fairly low calc and very low mag readings. I'm not sure how to process this or where to go from here.

 

[slingfox]

@Randy Holmes-Farley @ReneReef @Fish Fan

So my salinity results have confused me even more. I have left my refractometer as is, I have not adjusted its calibration at all. Currently my tank reads ~32.5 PSU. The two separate "Continuum" samples I have that are advertised as 35 PSU are both reading at ~37.5 PSU right now. I went ahead and made a sample sample per Randy's guide with iodized salt and RODI water and that read ~38 PSU.

If I recalibrate per those methods, then I would need even less salt which does not add up considering my fairly low calc and very low mag readings. I'm not sure how to process this or where to go from here.

Recalibrate your refractometer using the DIY solution. The data you cite above says that your tank salinity is way too low which is what everyone who replied above expected.

 

[Kalebos]

Recalibrate your refractometer using the DIY solution. The data you cite above says that your tank salinity is way too low which is what everyone who replied above expected.

I'm confused. Don't my results suggest that my salinity is high? If I recalibrate the refractometer which appears to be reading high currently wouldn't it require less salt to reach my target salinity?

 

[Kalebos]

I'm confused. Don't my results suggest that my salinity is high? If I recalibrate the refractometer which appears to be reading high currently wouldn't it require less salt to reach my target salinity?

Nevermind. I've only been home from work for a bit and my brain wasn't functioning right. My synapses are firing correctly for now.

 

[slingfox]

Nevermind. I've only been home from work for a bit and my brain wasn't functioning right. My synapses are firing correctly for now.

Yes, the salinity calibration can be very confusing but if you think about it long enough it will become clear