Salifert??

JustinM

New member
Is there anyone else having lots of trouble with the consistency of salifert? Months ago I had problems with the Alk kits reading from 6dKH to 11dKH all the time. I switched to Elos and the readings have been much more stable.

Well, I was getting low on my Cal test kit and the LFS didn't have an Elos one so I decided to give Salifert another try. I took a reading of my almost empty kit and got 400ppm, and then I took a reading of my new kit and got 460ppm. I thought this was an error so I redid both test kits, got the same on my almost empty and got 480ppm on my new.

I understand that there is going to be a much larger margin of error in hobby grade test kits, but this seems to be a little too much. What is my calcium I wonder? I hate bashing vendors and what not, but this is not cool. Especially if you are going to pay almost $30 for something that doesn't work. If I would have know this, I would have just put the money in my kids piggy bank. He could make better use of the money and not have bought something useless and he is only 2.

Sorry for the little rant, just needed to vent. Thanks.
 

disc1

-RT * ln(k)
Your older kit may have seen some evaporation from the titrant leading to lower readings. I don't think a 20% difference is anything to get too excited about. Your calcium is somewhere in the low 400's.
 

Sps Dream

New member
We have 4 salifert ca test kit with my friend. Two of them expired 2015, the other two 2016, we tested same aqurium parameter with these four, we had 4 different parameters ( from 400 to 500 ). I'm sure if we had six, we had six different parameters. So you are luckier than us :).
 

JustinM

New member
Well thanks for the replies. 20% does seem a little high though for a change. That means that if I'm reading 400ish I may really have 320ish. I don't think that a 20% margin of error is healthy for sps. JMO opinion though. Their test kits should read within 5% of one another, not 20%, whether they are accurate or not.

My test are exactly 1 year apart expiration date wise. Figuring that they put about a years worth of test in their kits, they shouldn't differ that much in 1 year. Maybe over 5 or so. We strive for stablility in our systems, not instablity.
 

disc1

-RT * ln(k)
If you need that level of accuracy, then you might want to consider using a seawater standard to standardize your kit against. Then throw away the instructions and do some real chemistry and do the math yourself.

Measuring against the known standard, take note of how much titrant was used. Now divide the standard value by the amount of titrant you used. When you test your tank water, multiply the amount of titrant you use by that number to get the value in your water.

The salifert kits are very precise. Notice that while the two kits you compared didn't agree with each other, they did agree with themselves when you re-ran them. So if you standardize the kit yourself, then you know you have something that is both accurate and precise.
 
David, I assume an IAPSO Standard Seawater solution may work for calibration, but have seen no place that sells it. Do you know where one could purchase a proper seawater standard fro the various ones we are interested in? :)
 
I assume you could make your own standard but precise equipment would be necessary. I'm not sure exactly what the parameters come in at using this:

An Artificial Seawater Recipe

For those who are interested, the following artificial seawater recipe is taken from "Chemical Oceanography" by Frank Millero. It makes a recipe that matches 35 ppt seawater in terms of major ions, but does not try to match all minor and trace elements, most of which will be present as impurities in the major elements.

23.98 g sodium chloride
5.029 g magnesium chloride
4.01 g sodium sulfate
1.14 g calcium chloride
0.699 g potassium chloride
0.172 g sodium bicarbonate
0.100 g potassium bromide
0.0254 g boric acid
0.0143 g strontium chloride
0.0029 g sodium fluoride
Water to 1 kg total weight.
 

JustinM

New member
Ok, again thanks for the replies. Call me ignorant but I wouldn't even know where to buy half of any of that list. All I see is salt, roach killer, and baking soda. I don't know what any of the other things are. Chemistry was the only class I have ever failed, and it's been 17 years since I have taken it too, granted I did get a B the second time I took it.

Thanks Cliff and David. It sounds like the best way to use our test kits though.
 

disc1

-RT * ln(k)
I'm putting up a new thread in a minute on how to do it. I don't know where to get IAPSO standards, but I know I've seen RHF recommend a standard. Some test kits come with them.

EDIT: I found the link he gave me but it's broken.
 
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disc1

-RT * ln(k)
Many test kits come with standards. You will be limited by their accuracy, but it would allow you to keep kits matched up.
 

hedgedrew

New member
the new salifert ca tests are def high thats the one with smaller powder spoon and darker in color ya 420 becomes 480 or 500 I'm getting better measurements out of digital titration kit from hach salifert read 500 hach said 450 460 on other hand because that is so precise its really hard to know how blue the sample needs to get before end of the test i can see range of outcomes from 440 to 460 as you turn the titration
 

bertoni

Premium Member
If the Hach says 450 ppm and the Salifert says 500 ppm, I'd be happy if the real level were anywhere between the two, and I wouldn't worry about the difference. I'm not sure which of the two might be more accurate in saltwater.
 

reefgeezer

New member
IME, much of the inconsistency comes from determining the end point of the the test. Don't hate me for this but I'll admit I rarely get that far in the tests anyway. I generally add a few drops at a time and stop when the color changes. I know, the true end point reading is a higher or lower, but I don't believe the difference would affect the decisions I make. Why waste the reagent to complete the process?
 

disc1

-RT * ln(k)
IME, much of the inconsistency comes from determining the end point of the the test. Don't hate me for this but I'll admit I rarely get that far in the tests anyway. I generally add a few drops at a time and stop when the color changes. I know, the true end point reading is a higher or lower, but I don't believe the difference would affect the decisions I make. Why waste the reagent to complete the process?

Yes, you're right. Many people tend to over or under titrate these tests. Finding an end point is a bit of an art and one of the trickier things to teach in an analytical lab class.

I think another large source of error is the measuring equipment they give us with the kit. Basically, with a salifert kit, you get a 3mL or 5mL BD syringe. The markings on the side of those things are not really intended for use with quantitative measurement. I mean there's a pretty large margin of error involved right there. If your sample size may be off by 10% or more, then there's no hope of getting an accurate result no matter how good you are at running the test or how good the reagents are.
 
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