How do I reduce alkalinity?

[jharn]

I have a RS Reefer 350 tank with a variety of soft corals and a couple of fish.  I’ve been having a hard time managing my alkalinity and nutrient levels.  I‘ve been doing weekly 15% water changes for the past couple of months but today’s alkalinity test showed 14.2 dKH using a Hanna tester.  Calcium is consistently around 480 mg/l using API test kit.  Magnesium is around 1425 mg/l.  I’ve always used Instant Ocean salt, but just got some Red Sea salt (Blue Bucket) and am planning to start using that in the future.  Anything else I should try to bring the alkalinity down to the usual 8-12 range?  Would it help to add some LPS or other hard corals?  I’m concerned about the high alkalinity, even though the soft corals seem quite happy.
 

My NO3 levels have also been high (>24 mg/l).  I’ve been dosing with RS NoPox for the past 6 weeks and the nutrient levels are finally starting to drop with today’s NO3 level down to 4 mg/l.  PO4 is 1.7 mg/l, while pH is 8.5.  Seems like the NoPOx is working, so will be tracking nutrient levels carefully to bring the NO3 down to around 1 mg/l.

[DaJMasta]

How's your salinity?  If there's more salt in the water (over 1.026 sg or 35ppt), you'll end up with higher numbers across the board.  Could be that you've just got a bit more salt than normal.

Which IO salt, though?  I wouldn't expect the regular stuff to be able to reach those levels, really, though maybe reef crystals could?

[Origami]

Well, the good news is that your calcium and alkalinity are very nearly balanced (in the range of "balanced"), even though it's very high. What is your salinity and what device do you use to measure it? Is the device calibrated? It could be that you're just mixing your salt up too strong (concentrated)?

[jharn]

I try to keep the salinity around 1.026.  I use a refractometer that I got from Bulk Reef Supply.  Is calibration just a matter of zeroing the scale with RODI, or is there more to it?  I haven’t been doing that, so will calibrate it today when I do a water change.

[DaJMasta]

You want to buy a 1.026 calibration solution and calibrate it to that.  While there is nonzero value in calibrating to zero, by calibrating to a point much closer to where it will be used, it will be much more accurate, since generally, the farther from your calibration point(s) you are measuring, the less compensated the measurement will be for whatever nonlinearities the device has.

It's also easy for a refractometer to drift - I found mine drifted up a couple of ppt in something like 9 months even when handled gently - so it's worth rechecking for sure.

[jharn]

Thanks for the advice.  I checked the refractometer this morning and it was definitely off.  When I zeroed it with RODI, the tank salinity was closer to 1.028. Sounds like this might help explain my high alkalinity values. I’ll look for the calibration solution you recommended so I can get a more accurate reading.  Lesson learned, for sure.

[nburg]

Yeah, I would calibrate or verify calibration every couple water changes to make sure it doesn’t deviate. Also use a consistent light to check it as some light can cause the line to be blurry or cast a weird shadow. 

[Origami]

If, after calibrating, you find that your salinity is high, diluting with RO/DI water is a reasonable course forward. We can help calculate how much you need for this if you're able to tell us your salinity and approximate the net gallons in your system (accounting for rocks and other things that displace water).

Sent from my SM-N976V using Tapatalk

[jharn]

I just checked my salinity again after calibrating the refractometer with Pinpoint Salinity Calibration Fluid That I ordered from BRS.  It’s a 35 ppt solution and after adjusting the refractometer my tank reading was 36 ppt.  My tank is a RS Reefer 350, which has a total volume of 91 gallons (display=73 gal; sump=18 gal).  I’d estimate the net volume, less rock and sand, to be about 80 gal.  Any suggestions on how best to reduce the salinity are much appreciated.  

[howaboutme]

Do you want to keep your salinity at 35 (1.026)? If so, I'd just make sure your new saltwater is at 35ppt and then just do water changes. 35 or 36 is so minor. If you ever do monitor salinity via a controller, you will see it fluctuate throughout the day. Once you see that you will know that any snapshot of your salinity via a refractometer is just that and you start to not worry about exactness.

[menglish]

If you are dosing Kalk or 2-part or a CaRx, stop dosing and allow it to come down.

[nburg]

59 minutes ago, jharn said:

I just checked my salinity again after calibrating the refractometer with Pinpoint Salinity Calibration Fluid That I ordered from BRS.  It’s a 35 ppt solution and after adjusting the refractometer my tank reading was 36 ppt.  My tank is a RS Reefer 350, which has a total volume of 91 gallons (display=73 gal; sump=18 gal).  I’d estimate the net volume, less rock and sand, to be about 80 gal.  Any suggestions on how best to reduce the salinity are much appreciated.  

 Reducing salinity is easy, either do water changes with 35ppt or remove a liter of saltwater a day and replace with RO fresh water. 

[therootcause]

Hello, 

 

Was the calibration fluid brought to tank temperature during calibration?  (I also have wondered if the refractometer needs to be brought to tank temperature during calibration.  Example, my basement is 67 degrees year round.  If I float a solution at 77 degrees then pipette onto the 67 degree refractometer, surely the liquid becomes closer to 67 degrees before I have a chance to even look through the viewfinder.)

 

I think that it has been widely discussed that IO salt can have varying alkalinity but has been found to mix at 15dk.   Could it be that your frequent water changes are actually the cause of the high alkalinity.  Have you tested the salinity and alkalinity of newly mixed salt water at tank temp?

 

-Adam

 

Edit:  I have submitted a product question to BRS regarding the temperature requirements in order to accurately use Pinpoint Calibration fluid. (fluid temp and refractometer temp)

Edited October 21, 2022 by therootcause