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is bottled De-Ionised water bought from a supermarket suitable for calibrating a refractometer? - I'd use RO, but I have a reading of about 5 TDS.
i would doubt if that has a zero TDS reading either - be interesting to check it though with a tds meter
not too sure... but there are silicates in bottled water so i would 'almost' certainly say no.
your RO will be fine for calibrating your refractometer. Even tapwater with a TDS of 500 would read only about 0.001 high so your RO would be 100x better if I have my sums right.
FWIW my brother made me up a salt solution in his lab that is exactly 30ppt, so I use that to calibrate and validate mine.
JasandJules
03-01-06, 13:20
Originally posted by danny@Jan 2 2006, 20:54
FWIW my brother made me up a salt solution in his lab that is exactly 30ppt, so I use that to calibrate and validate mine.
Everyone hates a smarta£$e!! ;)
he he! - hey, I've now discovered that I have been running my SG at 1.028 for the last 2 years! - don't see any ill effects mind....
incidentally, I accidentally left my fan running overnight about a week ago (long story!). As a result, it dropped my tank temp down to 70f. Fearing the worst, I raised it back up to 75f by mid afternoon the following day. A week later and nothing seems to have suffered - not even any sign of WS.
JasandJules
03-01-06, 15:53
TBH mate, I am not surprised 1.028 was fine, I was running our reef at 1.030 for ages with a swing arm. IMO/E the stability is the important bit. I was adding water change water calibrated at 1.025 according to my swing arm, which matched that of the tank.. Sooo, no huge SG variance in a day, inverts happy... Stability is more important than pinpoint accuracy in respect of SG IMHO.
Not so smart really :blush: Just to add that my refractometer is a recent purchase and has come about as I realised that my old swing arm was no longer accurate.
It used to be within one point of my LFS refractometer but I was shocked to find out it had drifted 3-5 points away :(
So over the last coulpe ofyears I reckon my tank has gradually gone from 1.025 upto 1.031 or more.
I am gradually lowering it and at present it is at 1.029 and everything looks alot better.
At the highest level I was aware that something was wrong but it took me too long to realise what. So I am sorry to say that I lost a couple of hard corals as a result.
Originally posted by danny@Jan 2 2006, 20:54
your RO will be fine for calibrating your refractometer. Even tapwater with a TDS of 500 would read only about 0.001 high
Danny,
This is one (among a few others) which has mystified me about refractometers. Why the need to calibrate with RO when tapwater is as you say likely to be far better than 500 ppm and we are trying to measure 35,000 ppm - probably an error smaller than the refractometer can hope to measure.
In addition to which the calibration point is so far away from the one we want to measure......
Since you have a decent calibration fluid, any chance of calibrating your refractometer with tap and RO and comparing the result ? I'd be very curious.
It may be that the error on calibration gets magnified the higher the reading. Eg I would guess that it measures the ratio of the refractive index of the saline solution to pure water, rather than the absolute difference. That would be quite different from a TDS meter, and would mean that the error gets scaled up.
Even so, I do suspect that the makers are introducing an unnecessarily strict procedure to create the impression of accuracy may not exist.
But it's just a suspicion and I can certainly see reasons why my cynicism could be leading me astray. I'd love to know the truth.
Oh, and yes, getting a 30 ppt calibration fluid certainly makes you a smart ass. I'd like to think that I'd have done the same. :lol:
kim
Stability is more important than pinpoint accuracy in respect of SG IMHO.
good point - planning to lower it gradually to 1.025.
Oh, and yes, getting a 30 ppt calibration fluid certainly makes you a smart ass. I'd like to think that I'd have done the same.
what do they use to calibrate the calibration solution then?! :wacko: :lol:
julesandsand
04-01-06, 10:27
I think you'll probably find that the guy in the lab uses deionised water to prepare the calibration solution.
Originally posted by clippo@Jan 4 2006, 09:37
what do they use to calibrate the calibration solution then?! :wacko: :lol:
Weighing scales. 30 g per L in this case.
sorry, I was being facetious.
Kim
I am going to get some 35ppt fluid too ;)
Actually by calibrating with RO and then verifying it with the 30ppt fluid it came out spot on. :thumbsup:
Tap water with a TDS of 500 gave an SG reading of between 1 and 1.001, although it is a narrow scale so to be accurate within 1.0005 is tricky by eye. In theory it should be 1.0005 shouldn`t it?
TBH I am not worried about being out by a point or two either way. What it important is that now atleast I can calbrate this piece of kit regularly so that I don`t end up where I was before. ie gradually increasing salinity.
Danny
Originally posted by danny@Jan 4 2006, 23:13
I am going to get some 35ppt fluid too ;)
Show off ! ;)
:lol:
You could make a nice turn buying a kilo of sodium chloride, getting your brother to divide it into precise 35g lots and selling them on here. Your brother could keep the surplus 20g as a reward. Tell him it's nice on chips ! :P
Then anybody who can measure a litre of tapwater to reasonable accuracy (that's not so tough) would have a nice calibration fluid.
Oh for a decent set of lab scales..... :(
kim
I could knock you up a calibration solution Kim (UKAS accredited lab) pm me if interested
Chris
:thumbsup:
I was gonna offer also... anyone else that want some calibration solutions (18.2 megaohm water and a 30 ppt soln) let me know...
sittingbourne... you work at the science park chris ??
coral garden do salinity calibration solution here (http://www.thecoralgarden.co.uk/product_info.php?cPath=24&products_id=575&osCsid=622adf96ec2798b683ee9f489101115d) for £2.75
Well, My brother knocked up a 35 ppt sodium chloride soloution (which was made by mixing 35 grammes of salt (dry) with 965 grammes of water ;) )
I calibrated my Deltec refractometer with RO to read zero and then tried the 35 ppt fluid. It was spot on :thumbsup: so looks like a decent bit of kit. Certainly better than my swing arm which was 5.5points out :o
Hi Ickypimp, no at the East Malling Research Institute, I used to work at the Science park back in the days when it was the Shell Research Centre!!
Chris
:thumbsup:
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