Magnesium - How low is too low

[EeyoreIsMySpiritAnimal]

Get one of these and you're set for life (assuming you don't break it, lol). No calibration needed, only slight calculation for temp above/below 77F.
https://www.bulkreefsupply.com/high-precision-hydrometer-tropic-marin.html

 

[Narideth]

Get one of these and you're set for life (assuming you don't break it, lol). No calibration needed, only slight calculation for temp above/below 77F.
https://www.bulkreefsupply.com/high-precision-hydrometer-tropic-marin.html

Oof, I can't take this stress, lol. I already ordered a new refractometer, but I've also ordered the high precision hydrometer. Can't go wrong with redundancies.

In the mean time, I mixed a small batch of higher salinity water based on the two not quite right measurements I have, and did a small (5ish%) water change in the tank to help boost it a little until I get the new devices. It's imprecise, but they're really suffering and the salinity needs to start coming up.

On the up side, apparently I can use my magnesium test to approximate salinity in the mean time! :rolling-on-the-floor-laughing:

 

[Narideth]

Now I'm really hoping the pods I put in a few days ago survived. The salinity would have been around 1.018-1.020ish according to the LFS readings and some generous assumptions on evaporation.

 

[Nick Steele]

I would personally take your ato offline and add salt water for evap for a couple days and see where that takes you. Measure salinity each day!

 

[Spicy Reef]

This is a great thread, love the interaction and resolution - NICE!

 

[ptrick21186]

Did some tests based on this conversation. I made up a batch of salt water using Reef Crystals. Calibrated my refractometer and tested water. Came in at 35ppt. Rechecked calibration afterwards still good at 35. Reef Crystals states on the label that at 35ppt you should have a mag level of 1345. Checked the mag level using Aquaforest TestPro test kit (not expired) and got 1170. Did another test using the reference solution provided in the test kit (1310+/-1%) and got 1320. Added mag to the clean salt water to bring it up to 1350 using the BRS calculator and rechecked the mag level. Mag level after dosing was 1290.

So from this I'm pretty confident that 1. My salinity is being measured properly. 2. My Mag test kit is fairly accurate. And 3. Reef Crystals is coming in lower than their advertised mag levels. Also please note that my batch of salt water is roughly 5gals but the level was slightly over the line which could explain why the dosing calculation was off slightly.

Obviously Narideth you found your problem to be low salinity and a faulty refractometer. But I just figured I'd throw my findings out there as an FYI. Always test. Never trust the label. I'm glad I did this though because as previously stated I was starting to second guess some of my testing. Guess it's good to know I was right about what was happening in my tank but still sucks that I'm being screwed on Magnesium.

 

[Narideth]

Additional updates:

I'm so confused. I am convinced that my salinity was quite low, and the corals are already responding positively to the increase in salinity I've been adding. Allow me to list the number of times I've had the water tested though, and I'll explain my confusion.

I ordered a new refractometer, and two different calibration solutions with the same exact results and readings that were wrong. Any reading I get elsewhere is approximately .005 lower than my refractometers - and that includes other refractometers and hydrometers.

Tank water (at the time) Measured to 1.025 with my refractometer
LFS: refractometer: 1.020
Petco: refractometer: 1.019
-After calibration with two different calibration fluids-
My refractometer 1: 1.025
My refractometer 2(new): 1.025
My Fluval hydrometer: 1.024

Note: the Fluval hydrometer I picked up the same day, and I think it's just muddied the waters of my various tests since it was somehow off too.


Newly mixed water measured to 1.030 with my refractometer
Petco: Instant Ocean hydrometer: 1.024
-After calibration with two different calibration fluids-
My refractometer 1: 1.030
My refractometer 2(new): 1.030
My Fluval hydrometer: 1.030


There is a consistent drop of salinity recorded in every single test taken at outside sources, but all of my tests have been 'accurate' to the calibration fluids I've received. I received the second calibration fluid today and it's claiming the refractometers are on point. This is just about the weirdest series of events. Ultimately I have a high precision hydrometer coming in from BRS tomorrow, but the mysteries continue. Why can't either of these refractometers be calibrated with the solutions? I've begun to doubt my knowledge of how to use these devices.

 

[ptrick21186]

If 3 different devices are giving you the same reading after calibration I would have to play the odds and say that's your salinity.

 

[Narideth]

There are a total of six different devices giving readings. Three say it's low, three say it's good. The added magnesium test supports low salinity. The corals responding positively to increasing salinity also seems to support it.

You see my confusion though.

The LFS is Coral Corral and they have hundreds of corals in a dozen bins, tanks everywhere, just, it's a huge store. I trust their reading, especially since I watched the guy calibrate his refractometer before taking the reading.

 

[Salty_Northerner]

I respectfully suggest your salinity is way low because there is no way that IO and Reef Crystals would be giving magnesium that low. The salinity being too low is probably what is annoying your hammers.

I suggest getting a TM High Precision Hydrometer to measure your salinity. They don't require any calibration and are essential for cross checking other salinity devices calibration. Just make sure you buy as well, the tall plastic cylinder they sell for it, to make ta

.

 

[Dennis Cartier]

When your TM hydrometer arrives, all will become clear. Just keep in mind it is calibrated at 25C/77F. So if your water varies from that, you will need to use an online calculator to adjust the reading to your water temperature.

 

[Randy Holmes-Farley Verified Community Expert]

What exactly are you using to calibrate the different devices?

 

[Tcook]

I would get an accurate scale off amazon and make you own calibration fluid that Randy has the recipe for in his forum. My TM hydrometer was even off by a bit. The small bottles of calibration fluid purchased online have been horrible imo.

 

[Narideth]

What exactly are you using to calibrate the different devices?

I purchased two liquid calibration fluids from online. The first was 'AccuBrate Refractometer and Hydrometer Salinity Calibration Fluid' from Aquatic Experts and the second, 'Continuum Reagents Refractometer Calibration Standard' from Continuum Aquatics.

Neither of them had like... a seal, which is weird. I had considered the scale and mixture myself, just hadn't gotten there just yet since I pulled the trigger on the high precision hydrometer.

 

[Narideth]

Holy heck this thing is huge! I had no idea I was buying something the size of a model rocket lol.

So, if I can trust the TM hydrometer as the final say, things were indeed out of balance. I've added quite a bit of higher salty water to the tank to bump up the salinity over the last two days, and the hydrometer is putting it at 1.0255, I was able to calibrate my refractometer based on that number, and it was .003 degrees out of calibration from what I'd already adjusted it (about .003) for a total of about .006 too low.

No one in this tank is happy, but I'm going to give it some time and some stability and hope the corals don't die on me. My hammers are showing serious tissue recession around the bases, but this was likely going on for a while now. Snails, urchin, and hermits all seem to be doing well.

What a crazy ride. Thank you to everyone who helped, chimed in, directed and commiserated. I'll post updates if there are any further.

 

[Narideth]

As a last note for the original topic of this thread: Magnesium is now at 1200 :upside-down-face: