Another Victim of Refractometer...

[hilde123]

I have been naive for the last 20 years thinking my refractometer was a reliable tool to check salinity. I just did my 3rd Fauna Marin water analysis test over the last year and I guess this one was more comprehensive then the one I typically do and checked basic values which included salinity. To my great surprise it indicates my salinity is 30 ppt and I have checked monthly for the past several years and it is rock solid at 35 ppt from refractometer. In fact I tested all my values the day I made the ICP sample for comparison. Since I use ATO and calc reactor I rarely have to make any adjustments to meet ideal salinity. With a little internet research I see the refractometer and using RO/DI to calibrate isn't really the proper way. I'm going to make up a known solution of 35 ppt tonight and check but I'm sure the ICP test is accurate... In doing my reading it looks like Hanna pen is way to go so I went ahead and purchased one of those for future use. My question is how slowly should I raise. Calculator says I need to add 9.5 pounds to get to 35 ppt (~200 gallon system). Also, how much should I expect my alk and calcium levels to increase in raising salinity noting they are already on the high side. Also, I should note tank is full of SPS, LPS, anemones, and clams. Attached is the water analysis.

 

[exnisstech]

Just a heads up in the Hanna. I've had two and they both read 0.002 low when calibrated with Hanna solution. I've seen others report the same. Others say they work fine so.... If you want something affordable and reliable never needing calibration maybe look at the TM hydrometer. I use one and use water tested with it to calibrate my refractometers.

 

[BryanM]

This is the way: TM hydrometer.

 

[fryman]

My most reliable gut check for salinity frankly is that I always use the same salt, bucket, & scoop to mix fresh saltwater. I use IO and a scoop/bucket that I know from years of use will mix to 35ppt. If I ever measure variation more than +/- 1ppt from that freshly mixed bucket, something is wrong.

I don't need to measure the freshly mixed buckets, but use it to gut check my refractometer. I prefer digital refractometer because it's so fast and easy. I have a milwaukee

I've heard people report that diff salt batches mix to diff salinity but that's not been my experience. If there's a difference between batches it seems to be low (within 1ppt)

 

[hilde123]

I guess I am just a tryhard! I test my salinity when I do water changes and try to adjust the amount of salt I add to keep my tank at the target salinity. I loose some salt to skimmate so I know I'm always going to have to make some adjustments. All that effort to make sure I get to where refractometer shows I'm at 35 PPT when I'm actually at 30 PPT. Not I got the 12" long glass hydrometer so I wont make that mistake again! BTW is was identical to the ICP test results so I can trust it!

 

[13rodo]

This is the way: TM hydrometer.

I use a TM hydrometer as well and then calibrate my hanna to that same water for spot checking.

 

[fryman]

I guess I am just a tryhard! I test my salinity when I do water changes and try to adjust the amount of salt I add to keep my tank at the target salinity. I loose some salt to skimmate so I know I'm always going to have to make some adjustments. All that effort to make sure I get to where refractometer shows I'm at 35 PPT when I'm actually at 30 PPT. Not I got the 12" long glass hydrometer so I wont make that mistake again! BTW is was identical to the ICP test results so I can trust it!

To clarify, I test display salinity as well every week and adjust accordingly, but I also do a sanity check against a freshly mixed 5gal bucket.

So I'm confident I would detect if my refractometer was off by 5ppt. If it read 40ppt or 30ppt (5ppt too high/low) from a fresh saltwater bucket, I'd know something was wrong.

 

[slingfox]

I have been through three Hanna salinity checkers. Nice to do quick spot checks but I would not rely on it as your salinity reference. Most reliable and simple option is the TM Hydrometer.