Low Tank Parameters - IO Salt

[therealraf02]

Howdy,
I’ve been having some interesting test results for my reef tank lately. For some context: i battled a pretty bad dino outbreak due to my nutrients bottoming out. I did the whole blackout shebang, fed more, stopped waterchanges, did manual removal, etc, and eventually got rid of the dinos and my tank has no signs of it any more.
I just did my first water change on my nuvo 20 in a while today, i’d say around 4 gal.
I’ve noticed before, and still see consistently low levels of calcium, alkalinity, and magnesium. (Well, i just got my salifert magnesium test today).
Here are some test results: (all are using salifert)
2/9
390 calcium
1.024
Alkalinity 8.0

2/23
Alkalinity 7.7
375 Calcium
1.025

5/4/25
dKh 7.9
Calcium 350ppm
1150 ppm Magnesium

5/6
Alkalinity 7.8
Calcium 325ppm
Mg 1170 ppm
1.025

I use instant ocean, the regular kind.
Today, I tested my saltwater reservoir (10 gallon brute) and here are the levels:
Ca 325ppm
Mg 1000ppm
Alk 9.3ppm

Don’t these levels seem weirdly off?
Would it be a bad idea to use a different salt? I’m running a mixed reef — 4 hammers, 1 frogspawn, some gsp on my back wall, a small poci colony, a stylo frag, a medium sized monti cap, and a small encrusting monti frag. And a zoa rock, 4 rfas, and an encrusted plate coral.

I have some stony frags coming in tomorrow and although I know these levels probably won’t kill them especially since they’ll most likely be going up over time due to more frequent water changes (although my mixed water seems to be suspiciously low in levels)… i still want to have as optimal an environment as I can given this context. i have a small bottle of all for reef, would it be an unwise decision to dose a little bit to get the levels to go up?

 

[bubbgee]

I don't rely on water changes completely for elements. I have 2-part ready to go as well as individual elements in case the numbers are off. That's the nature of things. Salt can be inconsistent as advanced reefers will notice.

 

[therealraf02]

Hmm interesting, i’ll look into AFR dosing or even individual calcium/alk/mag dosing

 

[rtparty]

Your refractometer needs to be calibrated. Your salinity is low which leads to all parameters being low like this

 

[therealraf02]

Your refractometer needs to be calibrated. Your salinity is low which leads to all parameters being low like this

Hmm didn’t think of that honestly, i did calibrate it with a diy calibration solution i found on here but I’ll try to find a premade one or a hanna checker to cross check

 

[rtparty]

Hmm didn’t think of that honestly, i did calibrate it with a diy calibration solution i found on here but I’ll try to find a premade one or a hanna checker to cross check

Randy’s DIY solution is the best way to go IMO. The premade solutions are often bad

 

[Randy Holmes-Farley Verified Community Expert]

I agree low salinity is likely. I would also add that 1.024 and 1.025 are already lower than average ocean water at 35 ppt, and even if properly calibrated, the refractometer will have some uncertainty in accuracy.

Example:

Ocean water at 35 ppt (sg = 1.0264)
Magnesium = 1280 ppm

At sg = 1.025 the value is 1212 ppm

At sg = 1.024 the value is 1164 ppm

 

[therealraf02]

I agree low salinity is likely. I would also add that 1.024 and 1.025 are already lower than average ocean water at 35 ppt, and even if properly calibrated, the refractometer will have some uncertainty in accuracy.

Example:

Ocean water at 35 ppt (sg = 1.0264)
Magnesium = 1280 ppm

At sg = 1.025 the value is 1212 ppm

At sg = 1.024 the value is 1164 ppm

Hi! My tropic marine high precision hydrometer just came in today. My salinity in the tank is currently at 1.0255, right in the middle of the 25 and 26 at the circle dot. I think that rules out salinity? Temp is at 77.4

 

[Randy Holmes-Farley Verified Community Expert]

Hi! My tropic marine high precision hydrometer just came in today. My salinity in the tank is currently at 1.0255, right in the middle of the 25 and 26 at the circle dot. I think that rules out salinity? Temp is at 77.4

I’d first raise salinity to 35 ppt (sg = 1.0264). That will raise all parameters (except pH and ORP) by 3.5% and then make any additional corrections as needed.

Fir example, the magnesium at 1170 ppm will become about 1211 ppm from the salinity boost.

 

[therealraf02]

How would you recommend I raise the salinity to 35ppt?

I’d first raise salinity to 35 ppt (sg = 1.0264). That will raise all parameters (except pH and ORP) by 3.5% and then make any additional corrections as needed.

Fir example, the magnesium at 1170 ppm will become about 1211 ppm from the salinity boost.

thanks a lot!

 

[Bohemian Waxwing]

The patient way I’ve used is make a small batch of higher salinity water, remove some from your tank, then replace with the higher salinity water.

I have a 60g and I use a measuring cup that holds 8 cups. I do it once or twice a day until I get the reading I want.

When I ran softie tanks I would just make a salt slurry and add it. Faster but also a sharper increase.

 

[Randy Holmes-Farley Verified Community Expert]

Top off for evaporation with salt water for a few days. :)

 

[Red_Beard]

Top off for evaporation with salt water for a few days. :)

^^this. Or just add some saltwater. It will evaporate down to normal and give you a gradual salinity increase until it gets back to where the ato kicks back in.

 

[Bohemian Waxwing]

Top off for evaporation with salt water for a few days. :)

I did this but then forgot to swap my ATO back to RODI :( ended up at 1.030 from 26. Oops!

 

[therealraf02]

Thanks for the advice yall.
I added some extra salt to my water change water (about to do a wc rn) and the salinity measured to about 1.028. I did not expect the salt to be that high however I don’t think it should cause any problems unless the water change is huge right? The tank is an IM Nuvo 20, and I’m going to do about a 2 gallon water change. How much would that impact the salinity of the tank?
Thanks!

 

[therealraf02]

Thanks for the advice yall.
I added some extra salt to my water change water (about to do a wc rn) and the salinity measured to about 1.028. I did not expect the salt to be that high however I don’t think it should cause any problems unless the water change is huge right? The tank is an IM Nuvo 20, and I’m going to do about a 2 gallon water change. How much would that impact the salinity of the tank?
Thanks!

Water is now 1.0256!

 

[Red_Beard]

Dont make waterchange water with extra salt, just add an extra pint of regular salt water and let it evaporate down, it's a lot more controllable and predictable, and you can do it whenever.

 

[therealraf02]

Dont make waterchange water with extra salt, just add an extra pint of regular salt water and let it evaporate down, it's a lot more controllable and predictable, and you can do it whenever.

Tru, thanks!
Also, i’m struggling to wrap my head around the math. My water change water was 1.0278, i changed two gallons of water from the tank which was at 1.0255. It only went up to 1.0256, when it should have gone up to around 1.0258, using the formula
D = (A (t - r) + C* r) / t
A = 1.0255 (starting salinity)
C = 1.0277 (new water salinity)
D = 1.0256 (resulting salinity)
r = 2 gallons

t, or the tank volume comes out to 44 gallon..

 

[therealraf02]

Tru, thanks!
Also, i’m struggling to wrap my head around the math. My water change water was 1.0278, i changed two gallons of water from the tank which was at 1.0255. It only went up to 1.0256, when it should have gone up to around 1.0258, using the formula
D = (A (t - r) + C* r) / t
A = 1.0255 (starting salinity)
C = 1.0277 (new water salinity)
D = 1.0256 (resulting salinity)
r = 2 gallons

t, or the tank volume comes out to 44 gallon..

I am also using the tropic marin precision hydrometer in a graduated cylinder

 

[Red_Beard]

Oh yeah, just adding a pint simplifies that dramatically. You could even grab a before and measure again after it evaporates down and know precisely how much a pint adds for future calculations. Easily repeatable and you dont have to think about how much water you can change with the water you have mixed up.
The TM hydrometers are awesome. That is what i use too.