Instant ocean purple very low calcium?

[Miami Reef]

Salinity 1.026 tested with a calibrated Milwaukee refractometer.

The calcium is testing 355ppm with the salifert test kit.

My display tank is testing about 390ppm calcium, and I wasn’t sure why the calcium was so low. Either I’ve been reducing the calcium with each water change, or the Salifert calcium test is off.

The test expires 3/2027

Is it normal for instant ocean to test this low? Should I trust the readings and boost it with calcium chloride (my preferred solution)

Or should I be skeptical of the test kit? (my least preferred solution)

Edit:
I just purchased a new salifert calcium kit, and the calcium levels are showing 395ppm in the new saltwater and 410ppm in the tank.

I will assume the older salifert kit went bad for some reason. I knew it was smart to follow my intuition.

 

[Randy Holmes-Farley Verified Community Expert]

It used to be low, but I think the current spec is for it to be higher. Not sure what folks are seeing now.

 

[Miami Reef]

It used to be low, but I think the current spec is for it to be higher. Not sure what folks are seeing now.

Do you know of any saltwater calcium standards? I’d much rather buy a standard than a few more test kits. I have a feeling that the kit might be off. It’s illogical for me to assume the instant ocean is actually 355ppm. That doesn’t sound right.

I think I either need to get a standard or a few more calcium test kits. I need to know if the calcium value is real or not so I can make adjustments.

You are very logical. Tell me what the more science-based approach would be. I just want to know if my test is accurate before I start dosing large amounts of calcium.

 

[Malum Argenteum]

A year ago it ICP tested at 380ppm (here) when mixed to 35.4ppt. More recently a test kit found 400ppm (here) when mixed to 34.5ppt.

Given the imprecision in measuring salinity, and in measuring calcium, there's no reliable way to compare other's results with yours except in a pretty wide range.

I add some CaCl to each batch of IO I mix, but I'm not too fussy about the exact calcium level. You could certainly mix a batch and add CaCl until you hit your target measurement.

 

[Miami Reef]

I just purchased a new salifert calcium kit, and the calcium levels are showing 395ppm in the new saltwater and 410ppm in the tank.

I will assume the older salifert kit went bad for some reason. I knew it was smart to follow my intuition.

 

[GlassMunky]

Salinity 1.026 tested with a calibrated Milwaukee refractometer.

The calcium is testing 355ppm with the salifert test kit.

My display tank is testing about 390ppm calcium, and I wasn’t sure why the calcium was so low. Either I’ve been reducing the calcium with each water change, or the Salifert calcium test is off.

The test expires 3/2027

Is it normal for instant ocean to test this low? Should I trust the readings and boost it with calcium chloride (my preferred solution)

Or should I be skeptical of the test kit? (my least preferred solution)

I’ve been seeing super low calcium and alk on purple box since December. Like alk of 6.5 and calcium at 350ish.
I recently started mixing half/half IO and Reef Crystals now and that’s been a lot better.

Edit to add: confirmed my test kits are correct with new ones and double verified by ICP test on the tank

 

[GARRIGA]

Do you know of any saltwater calcium standards? I’d much rather buy a standard than a few more test kits. I have a feeling that the kit might be off. It’s illogical for me to assume the instant ocean is actually 355ppm. That doesn’t sound right.

Hach has reference solutions.

 

[Mwatts12]

Salinity 1.026 tested with a calibrated Milwaukee refractometer.

The calcium is testing 355ppm with the salifert test kit.

My display tank is testing about 390ppm calcium, and I wasn’t sure why the calcium was so low. Either I’ve been reducing the calcium with each water change, or the Salifert calcium test is off.

The test expires 3/2027

Is it normal for instant ocean to test this low? Should I trust the readings and boost it with calcium chloride (my preferred solution)

Or should I be skeptical of the test kit? (my least preferred solution)

Same. Instant ocean purple. Mixed up for 24 hrs I get about 360 calcium / 1200 ish magnesium.

Have to dose a few hundred ML to the brute.