I also started with a hydrometer. Hydrometers shouldn't even be sold as a salt/sg measuring device. My refractometer was a real eye opener for me too. Hydrometer was way out.

Thanks for all the help so far! So I did an improvised DIY solution following the basis of the reefkeeping article. I used 1927ml of RO water, and mixed in 1/4 cup (73grams) of Salt... The salt was easy to measure with a measuring cup and I used another glass measuring cup to get 1900 ml of water, I used a syringe to add the final 27 mL of water so I'm fairly certain I was precise.

I did this mixture 3 times just to be certain I didn't screw up somewhere :lol:

Now, just to be sure when he says "Morton's Iodized Salt" he's talking about an American Brand name for table salt correct???

This mixture gives me the 3.65% ratio of salt to water I need to adjust to a 35 ppt reading on the refractometer. I took 3 readings off each batch, every reading of every batch was within .005 of 1.029 so I proceeded to adjust my refractometer to 35ppt or 1.026.

So, with all that done do you guys think I could be confident trusting the reading I'll take after supper?

Thanks and Cheers

You should get the Pinpoint fluid before you change anything. No rush, corals can thrive in a pretty wide range of salinity... as long as it's stable. If your tank looks good, don't mess with it! Refractometers should sold with a 35 ppt calibration fluid.:rolleyes:

Your math is right and the fact you got the same result 3 times is a good sign. It comes down to how precise your measures were, a good scale would work better than volume measurements.

Yep.

I think you should be fine. Please post the measurement you get with both devices now that you've calibrated, it sounds like they'll be pretty close.

Ok, so using my DIY calibration fluid as described above, here are my new results.

The refractometer out of the box tested the 35ppt solution at 39ppt, it tested my tank at a salinity of 40ppt. After calibration with the DIY fluid my tank tested at ~36ppt (sg1.027). so that sounds ok, it was 4ppt high. Still higher than I would like but a lot less earth shattering than my original reading of 1.030.

I adjusted the solution as per the article for a hydrometer as well and found that it supports the newly calibrated readings from the refractometer. It gave me an adjusted reading of 1.0265 for the tank water

So it seems that the calibrated hydrometer supports the calibrated refractometer and I can be fairly confident that my refractometer is now accurately reading salinity right?

Sort of disappointing to find that a $65 piece of equipment billed as a must have for reefkeeping was less accurate out of the box than a $10 plastic instant ocean hydrometer.

LOL that's how I felt when I first found out. Try using one for 2 years and then you find out it's been inaccurate all that time, and your little swing arm hydrometer that everyone snubs was actually reading more accurately.

Still, once you get them calibrated correctly they are indispensable.

So, this is interesting....


After deciding that the refractometer was off by using the home-made recipe discussed above, I decided NOT to make any changes until I could pick up a bottle of the pinpoint 53 ms solution and get a "third opinion". I'm glad I waited

When I calibrate the refractometer with the 53ms solution, I discovered that my home-made solution was off, and that my original calibration was correct! It now reads distilled water at 0ppt and the 53ms solution is 35ppt. So, I guess I can draw several conclusions

#1) It looks like I got a dead-on refractometer after all!

#2) It pays to check, double check and quite often triple check the calibration of stuff.

#3) I proved that I can make the wrong solution exactly the same 3 times in a row and all that it proved was none of my wife's kitchen measuring utensils are as accurate as they should be. My confidence in the next batch of gravy is going to be a little shakey :lol: :lol: