k2parkstar
Z&P Snob
I'd prefer hot water, and then rinse with RO
What have you done to your system today?
- Thread starter Dapple
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I'd prefer hot water, and then rinse with RO
redngold
Community Member
It has been at least a year. I may grab some fresh ro water right out of my filter and see if the refractometer is just off.
k2parkstar
Z&P Snob
You don't want to calibrate it with RO, you need to use a test solution.
Calibrating with RO is a REALLY BAD idea. There are tons of examples out there of people who have calibrated their refractometer with RO and it's way way off.
Scientifically speaking, it's much better to calibrate with a test solution within the range of the measurement that you want to make. Ideally you'd test with a range of different concentrations of salt solutions, some above 1.025 and some below it. But generally it's fine to calibrate with a test solution that's around 1.025.
I made some TDS solutions are 35 ppt NaCl and they're at Aquatic Marine. I think they still have some. You might call and ask. If they're the ones from me, then they're free. If they don't have one then I can bring you an aliquot at the next reef club meeting (if you remind me...because I will almost definitely forget).
Scientifically speaking, it's much better to calibrate with a test solution within the range of the measurement that you want to make. Ideally you'd test with a range of different concentrations of salt solutions, some above 1.025 and some below it. But generally it's fine to calibrate with a test solution that's around 1.025.
I made some TDS solutions are 35 ppt NaCl and they're at Aquatic Marine. I think they still have some. You might call and ask. If they're the ones from me, then they're free. If they don't have one then I can bring you an aliquot at the next reef club meeting (if you remind me...because I will almost definitely forget).
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redngold
Community Member
Thanks guys, I meant I was going to test my RO water just to see if the meter is off right out of the "tap" so to speak. It probably is due for a re-calibration either way.
You know...I was worried about my RO a while back and I made up some TDS solutions (three different ones, something like 5, 50, 500). I tested my RO's TDS meter and it wasn't too far off. It's a really good thing to check because having been around for a long time, I've seen several people whose tanks crashed because their RO unit went bad (typically something like the membrane breaking through). It's heart-breaking when it happens. So if you're at all worried, I'd definitely check into it!! Good idea.
Rob.D
Moderator
Mel, do you have any more TDS solution?
CoryC
Valuable Member
According to a university article on measuring salinity, refractive index,etc. and based on their table I was under the impression that 1.026 was the salinity of a 35 ppt calibration solution I use? Am I off? My salinity is stable 1.025 but if I'm wrong I guess it's 1.026, hopefully this isn't screwing with my coral.
k2parkstar
Z&P Snob
The article should have mentioned temperature as well, because specific gravity and salinity depend on temperature.
At 60 degrees F
35 ppt = 1.026 S.G.
At 70 degrees F
35 ppt = 1.025 S.G.
Unless your tanks are 60 degrees your tank is 35 ppt if your at 1.025.
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redngold
Community Member
Well it looks like my refractometer is the culprit! Straight out of my ro unit it is measuring .07. Which means my tank is actually a little low at .22(was measuring .29). Looks like I need to go by AM tomorrow and see if they have any calibration fluid.
k2parkstar
Z&P Snob
At least you know the problem. Hope it wasn't hurting your tank.
Yeah. Are there no more at AM?
Good reasoning.
I never say that my solutions are 1.025. I say that my solutions are 35 ppt NaCl. It's written on the tubes I give to people. It's up to you to make your own judgement whether it's 1.025 or 1.026 as I have heard conflicting information.
BUT if your tank is constantly running at 1.026 instead of 1.025, it's not going to make a bit of difference. I'm sure that's within the margin of error of the instrument anyway. If you think you're really measuring a difference of 0.001 on your cheap refractometer then I cannot help you anyway.
redngold
Community Member
75 and 24 are now at a stable .25 glad I caught it when I did. Went back to AM today with the family and picked up a torch and a green clown goby for the 24. Picked up a small piece of favia brain and some gsp for my 75.
Rob.D
Moderator
Glad you got things in order. Do you have a build thread or pics of your set ups?
OK, 35 ppt NaCl, right? I often wondered why your solution and my "homemade" one differed but after reading through Randy's article again I think I understand why. The refractive index of a solution of NaCl is not the same as the refractive index of seawater. According to Randy, you need 36.5 ppt NaCl solution to give you the same refractive index as 25 ppt seawater. So, if you're calibrating to 35 ppt on your refractometer with a NaCl solution, you're actually calibrating on the high side by about 1.5 ppt. What does this mean? When you then trust your refractometer and mix your salt water up to 35 ppt (1.0265), you're actually OVER this value.
If you use those swing-arm type SG devices, the error is actually higher. Someone please check my math. The article is here:
Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com
Dave
If you use those swing-arm type SG devices, the error is actually higher. Someone please check my math. The article is here:
Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com
Dave
redngold
Community Member
Nope I need to get some pics up of them. I;ll work on that tonight.
Dave, if you tell me what concentration of NaCl I should make, I'll remake the solution and give them out to everyone.
I would like to know what ppt NaCl is equivalent to 1.025 salinity on my refractometer. I don't have time to read that article today but I will definitely do it once I get back from out of town.
I would like to know what ppt NaCl is equivalent to 1.025 salinity on my refractometer. I don't have time to read that article today but I will definitely do it once I get back from out of town.
