Bad H20 salt batch?

Answer:

Kevin
Thank you for your email.
If this is true then it would be the first time that we have ever had the magnesium out of spec so it always makes me wonder.
We get many people who comment on it being in the 1200 level only to find that they have not been measuring the salinity properly or mixing the bucket but obviously what you are quoting is ridiculously low and could not be explained by such errors.

Could you perhaps answer me a couple of questions

1 - Are you quoting a low magnesium in your system or in the salt mix. (your comment on not having the salt bucket suggests the tank)
2 - What salinity are you mixing to and what sort of equipment are you measuring with
3 - How do you calibrate your salinity measuring equipment.
4 - what are the other parameters for the salt mix.
5 - which test kit are you using
6 - what size is your system.
7 - what type of coral stocking do you have

This will give us some idea as to how to answer your query

Regards
Stuart

Customer Response:

Thanks for your prompt reply Stuart, here's the answers to your questions:

1. Mg was measured in the mixing containers (32 gallon plastic tubs) after

mixing with powerheads for 24-36 hours. I began measuring the new salt mixes

subsequent to checking Mg in my tank when I began getting low Alk. readings

in the tank. Mg in tank was low, unusual results since I began using your

product a year and a half or so ago.

 A: I agree that your Mg should not drop when using our salt. I was of the opinion that mine was low last week as my test kit had run out but when I checked it was at 1380ppm.

One of the concerns that I have is that I do not know how good or bad the seachem test is for measuring magnesium as we have found a number that can be out by about 100 on the low side and recommend the Tropical Marine test as being the most reliable currently available.

2. SG of 1.025 measured with an Aquamarine Bio-Chem Division salinity

refractometer w/automatic temperature compensation.

3. Per manufacturer's instructions; last calibrated about 5 months ago.

A: It is most likely that this refractometer is a brine refractometer which means that it will measure a salinity about 1.5ppt down on what you think it is.

We have developed a true seawater version and I have written an article on the differences. http://www.theaquariumsolution.com/specific-gravity-salinity-and-its-measurement.

 You need to calibrate your unit much more regularly than you are now in my opinion. There is a possibility that this has drifted. Add to this the fact that it is a brine refractometer and you could be quite a way out on the salinity. This would back up the reason why you are measuring very low calcium too.

 Read the section on why we should not use the SG side of the scale as 35ppt salinity is actually 1.0264 and not 1.025.

4. Per my log,  mix in tubs average pH ~ 8.2, Alk 4-4.5 meq, calcium was

consistently on low side at 350 to 375, all measured with Seachem test kits;

Low Ca was not as much of a concern since it was not fatally low & easily

adjusted with Seachem product without raising SG.

 To bring Mg up to ~1350 it requires a lot of Mg additive which in turn shoots up the SG to 27 or 27+.

A: In the same way that you need to add a lot of magnesium to bring this level up then imagine how much you would have to miss out of a 1 tonne batch to get such a low level.

I still use a brine refractometer myself and adjust the number that I am looking for on the salinity scale 10 37.5ppt. You will find that this equates to 1.028 on your refractometer scale.

5. Again, Seachem test kits. I compare to reference standard supplied with

kits if I get a reading that looks suspicious.

A:I have no experience of this kit but would perhaps look at a check with a different manufacturer and ideally the Tropic Marine test

6. My system is a 265 gallon tank, 30 gallon sump, probably ~ 210 gallons

after discounting for live rock & coral displacement.

7. Stocking is heavy, combination soft corals & lots of sps. You can view

tank on Reef Central via link at

http://reefcentral.com/forums/showthread.php?p=15844252&posted=1#post158...

scroll down to view pics.

 Please have a look at this new information and feed back to me 

Regards

Stuart

Customer response:

Good Morning Stuart. Read your article, makes sense, however a few things came to mind - I recalibrated the refractometer  in middle of problem, Mg low before & after recalibration. But I guess the main point of logic is why would your salt mix tested fine for the first 5 -6 pails (at my readings of 1.025) then be low for the last 2? I'll go back & reread your article since there is much to understand in it. Pretty much every reefkeeper I know shoots for 1.025 with a refractometer. I suspect most hobbyists must therefore have a lower salinity than they think, in fact it may turn out that the most luxuriant reef systems attain their peak at lower salinity. Interesting implications! Kevin

DD Response:

Customer response:

Yes, the inner bag was intact. Thanks!