Refractometers
- Thread starter spiffergirl
- Start date
yeah, my swing arm has a small amount of salt precipitation on it. i know that definitely affects the already inaccurate results. why waste another seven or eight bucks when i could get a more accurate reading instrument that could last a lot longer?
i have been checking out marine depot dot com for refractometers, but there are so many choices.
i have been checking out marine depot dot com for refractometers, but there are so many choices.
I use a refractometer that I bought from Premium Aquatics for about $59 I think. It is accurate, extremely easy to use *read way way easier than a swing arm* and is consistent. That is what counts. I first used my swing arm which read 1.024 then I used the refractometer and it read 1.030 which is a huge difference. I calibrated the refractometer to distilled water before use so I know it is accurate. It is unlit and you drop a drop of water on it relplace the slide and look through the eyepiece under a light and presto..... sg and percentage all in one reading........worth every red cent it cost me.
There is an unspoken assumption thro' the hobby that refractometers are 'better' than hydrometers as they are more accurate - this is not always true.
For sure swing arm hydrometers are rubbish. Even with frequent cleaning to stop weighting of the arm, and sticking, theyare still hopeless and to be avoided.
The point to bear in mind is that of hydrometers, refractometers and even digital meters NONE MEASURES SALINITY DIRECTLY. All use a physical phenomena (in order density, refractive index, electrical resistivity) that can be linearly correlated to salinity, and then back out the figures from the correlation to give a salinity. However all these 'salinities' are an approximation due to accuracy of the tool and also all of these phenomena are affected by other phenomena, principally temperature, but for the digital readings also the exact seawater composition can make a difference.
From a practical point of view, what to do, what to buy. For a start, if you have a floating hydrometer don't necessarily thro' it away. I have a lab grade hydrometer (froim Brennan in the UK, redistributed by TMC, not available in the US tho' the equivalent is somewhere) that comes with a +- accuracy reading. This is very good, reliable, somewhat easy to use. Your floater might be as good as this , might not - you need to investigate by looking at it on the scale , or on the packaging. For the same price as my hydrometer I could get a refractometer from Marine Depot, STM or whoever for 30 to 50 euros/dollars. This is easier to use, and as lorna has worked out, has calibrated it's zero to distilled water successfully. To check it's accuracy at a real salinity you would need to compare it to a stock solution of 35 ppm salt mix. Normally at this price point the +- accuracy is either not defined, it is a little poorer than my hydrometers reliability, repeatability, but it is easier to use. To beat my hydrometer you will need to spend 200 dollars plus to get a more reliable calibrated refractometer, and you will also need to spend more time calibrating it.
For me the digital meters are not worth it. they need repeated calibration and careful cleaning. If you are using one as a computer controller then they are the only thing you can use, but they do require much maintenance then, wear out quickly and are still not 100% accurate for a good number of reasons.
For me most hobbyists can use either a refractometer or a decent floater. The differences are negligible
For sure swing arm hydrometers are rubbish. Even with frequent cleaning to stop weighting of the arm, and sticking, theyare still hopeless and to be avoided.
The point to bear in mind is that of hydrometers, refractometers and even digital meters NONE MEASURES SALINITY DIRECTLY. All use a physical phenomena (in order density, refractive index, electrical resistivity) that can be linearly correlated to salinity, and then back out the figures from the correlation to give a salinity. However all these 'salinities' are an approximation due to accuracy of the tool and also all of these phenomena are affected by other phenomena, principally temperature, but for the digital readings also the exact seawater composition can make a difference.
From a practical point of view, what to do, what to buy. For a start, if you have a floating hydrometer don't necessarily thro' it away. I have a lab grade hydrometer (froim Brennan in the UK, redistributed by TMC, not available in the US tho' the equivalent is somewhere) that comes with a +- accuracy reading. This is very good, reliable, somewhat easy to use. Your floater might be as good as this , might not - you need to investigate by looking at it on the scale , or on the packaging. For the same price as my hydrometer I could get a refractometer from Marine Depot, STM or whoever for 30 to 50 euros/dollars. This is easier to use, and as lorna has worked out, has calibrated it's zero to distilled water successfully. To check it's accuracy at a real salinity you would need to compare it to a stock solution of 35 ppm salt mix. Normally at this price point the +- accuracy is either not defined, it is a little poorer than my hydrometers reliability, repeatability, but it is easier to use. To beat my hydrometer you will need to spend 200 dollars plus to get a more reliable calibrated refractometer, and you will also need to spend more time calibrating it.
For me the digital meters are not worth it. they need repeated calibration and careful cleaning. If you are using one as a computer controller then they are the only thing you can use, but they do require much maintenance then, wear out quickly and are still not 100% accurate for a good number of reasons.
For me most hobbyists can use either a refractometer or a decent floater. The differences are negligible
Great explanation, Wayne. My hydrometer is not the floating type. Salt has precipitated onto the swing arm and inside the apparatus and soaking it has not removed it. Therefore, the hydrometer is completely off.
As far as accuracy, I am not whole-heartedly concerned because I am keeping fish only for the most part. At this point, I only need a reliable and simple refractometer. For the past three months I have been "winging it" and doing very small water changes very often adding the "approximate" amounts of salt based on prior changes. So far this hasn't killed anything. I know that I would like to treat my fish better, so I still have to purchase better equipment.
Thanks for your help. Where did you get your lab-grade hydrometer anyway, Wayne?
As far as accuracy, I am not whole-heartedly concerned because I am keeping fish only for the most part. At this point, I only need a reliable and simple refractometer. For the past three months I have been "winging it" and doing very small water changes very often adding the "approximate" amounts of salt based on prior changes. So far this hasn't killed anything. I know that I would like to treat my fish better, so I still have to purchase better equipment.
Thanks for your help. Where did you get your lab-grade hydrometer anyway, Wayne?
Actually mine was resold by TMC in the UK, but most people who want one in the UK go direct to Brennan who sell a variety of hydrometers calibrated to different temperatures with different accuracy tolerances. In Houston , or the US, I have no idea.
I'll give you a tip - more people I know, myself included, 'wing it' with 'approximate' amounts of salt in their change water. I stick in one 'mug' per 10 litres that gives me a 1.025 solution at 25C, presumably +- a little bit each time. In reality, if you thik about it, you might be 5 or 6 % out on salinity, on a solution you're going to perform a 10% change with. It might not be perfect, but frankly it is well within any reasonable tolerance level. In fact, even tho' you might spend a bunch of time faffing around tryingto make the perfect water to change with, you're now at the absolute limits of what any salinity measuring device can measure without spending hundreds of dollars on something with a tighter error correction.
I'll give you a tip - more people I know, myself included, 'wing it' with 'approximate' amounts of salt in their change water. I stick in one 'mug' per 10 litres that gives me a 1.025 solution at 25C, presumably +- a little bit each time. In reality, if you thik about it, you might be 5 or 6 % out on salinity, on a solution you're going to perform a 10% change with. It might not be perfect, but frankly it is well within any reasonable tolerance level. In fact, even tho' you might spend a bunch of time faffing around tryingto make the perfect water to change with, you're now at the absolute limits of what any salinity measuring device can measure without spending hundreds of dollars on something with a tighter error correction.
Wayne you are absolutely right as always. I usually add 1/2 c per gallon of Tropic Marin and it mixes almost always exactly at 1.025 or 35 whichever measurement you want. I am usually only out a bit due to the fact that I use 5g jugs of water and when I fill them they are not always exact.....I also figure that if I am out .005 or so in my mix 5- 10g out of 75 isn't enough to shock anything in my tank. I think they get more fluctuations from evap and top up. So far everyone is happy as my clam.......
I went with the refractometer as my husband wanted one as he was used to working with them through his work......I would still pick a floating hydrometer over a swing arm any day though.
I went with the refractometer as my husband wanted one as he was used to working with them through his work......I would still pick a floating hydrometer over a swing arm any day though.