Refractometer Help

[Mash2K]

I just bought this: http://www.drsfostersmith.com/product/prod...=1&N=2004&Nty=1

 

Anyway, for calibration it says to use "distilled water". I only had RO water. When I did the calibration technique per the instructions, it came out calibrated already. Then I tested my water which came out to .023 ppm and then I used my Instant Ocean hydrometer and it came out .028. Did I screw up the calibration? It just seemed like a huge differential.

[chvynva916]

My guess is your IO hydrometer sucks and was way off. You might have screwed up the calibration (it is possible), but search around and see how many people (including me) have had hydrometers that are waaaaayyyy off.

[bobioden]

I think you calibrated it right, and your hydrometer is off. You are going to want to increase it, but do is slow, over the next few water changes.

 

Bob

[SaltyDawg]

Hydrometers are usualy a few points off. Trust your refractometer.

[NCNBilly]

Pick up a gallon of distilled the next time you are at the grocery store. It's the cheapest thing you'll ever buy for your tank.

[cich1]

my refractometer test the same with distilled water as it does with ro/di water so you're probably okay, the reason they specify distilled is so you calibrate with a known pure source ie no sodium, hydrometers are calibrated at a certain temp. usally 60 d farenhiet i believe so if your not compensating for the higher temp it never will give a true reading. btw i had a IO hdryometer for about a week and yes it did suck

[Mash2K]

I tried distilled water and it came out the same.....spot on.

 

You were 100% correct.

[CodeToad]

There was a great article a while back in reefkeeping magazine about calibrating your hydrometer to 35ppt and zero. I bought a cheapie refractometer and suspected its results to be wrong. I compared it vs friends and LFS's SW with high end refractometers and the conductivity meters, and found my refractometer was way off. I returned it and purchased a more expensive unit and ran the same testing.

 

I would say test against a LFS or someone with a high end refractometer or even better a conductivity meter.

 

Check this out as well:

http://www.reefkeeping.com/issues/2004-06/...6/rhf/index.htm

[ViciousFishes]

I would go with the refractometer reading an IO hydro only cost $8 and are calibrated at a certain temp. Also what CodeToad said, it looks like you got the low end model so it might be a little off but it should be much closer to a true salinity reading than the IO hydro. You should have got a high end glass hydrometer, like the $25 model Dr.F&S sells. Their better then the low end refractometers and cost much less.

[lgreen]

my coralife hydrometer says my salinity is at about 1.023-1.024, my new refractometer (the 35.00 one from Dr. F and S) say 1.028. does that sound about right, has anyone had similar differences with the coralife hydrometers?

[Pinchy]

hard to say; b/c its only a 35 dollar refractometer i would be a little concerned about its true accuracy- like mentioned b/f bring it to LFS to compare w/ their refractometer if they have one; our store has one that cost around $150. there has to be some difference.

[willgr1]

i have the same refractometer, it works great. i have tested it against the known specific gravity of a few different water sources and it's been accurate everytime.