Test Kit Questions

[androal]

Reposting this question after re-writing it more clearly (I think?)

I recently bought two 20kg boxes of Korallen-Zucht reefers best salt mix. After mixing each box to a specific gravity of 1.26 at 78 degrees (using a freshly calibrated Milwaukee digital refractometer to validate), I measured Ca, Kh and Mg with following results (using brand new Elos test-kits):

Ca 370-390
Mg 1000 - 1200
Kh 10.5 - 12.5

The results vary significantly from what I've seen posted by others who use this brand. I'm dry mixing the salt before making it up and I'm using the entire batch to minimize any issues with "settling during shipping" of mineral content. The results were consistent between the two separate 20kg boxes of mix, but have read there's potentially a quality-control issue from the manufacturer who makes up small batches of the stuff at a time?

1-Why are there such significant variations in peoples published results from this salt mix? (or other's for that matter, I've also seen wide variances in the published results for other manufacturers mixes too)

2-Are others having similar issues with their test kits? I've seen people publish results from the same salt mix using different test kits and getting different results? Specifically, these are the issues I'm having with Elos:

Ca- While the test kit claims accuracy to 10mg, I seem to always have a question as to when the kit precisely "turns" from one color to the other (i.e. does it turn colors at drop 3 or at drop 4?) It begins to change after the 7th drop of Solution "œC". An 8th drop of Solution "œC" turns it completely, so I pull out solution "œD" for the finer calibration. After 7 drops of solution "œC", the color gradually fades between drops 3-5 from one color to the next. I'm not totally sure that is completely changed until the 6th drop from solution "œD", which does not make sense, as that would put it at 410, and the Solution "œC" clearly turns after the 8th drop, which is 400. Needless to say, I'm somewhat puzzled by people who are able to dial in their Ca at 440mg with a dosing pump and hold it there. Seems to me that this becomes more an art than a science for anyone using these kits to measure Ca? What am I missing? Why not just manufacture a salt mix that targets their "ideal range" to start with?

Kh - This one seems to be one of the more simple tests to run, which makes me think that that the numbers people are floating around for their salt mix test results must be true - for them. Having said this, there are alarmingly vast discrepancies from various posts out there on peoples experiences using same salt mixes (I've seen anywhere from 6-14 DKH published by various user's experiences with this mix). With the Elos test kit, it is consistently shifts colors between drops 22-24, but the precise drop number that changes the solution "fully" from blue to burnt orange is a bit more subjective. This widens my possible range to more like 21-25 drops for any given sample I take, depending on how well (or not well) I'm able to read the color change. These means that depending on how orange I think my kit reads, I'm measuring KH within a pretty broad range of 10.5 - 12.5. Makes me think that DKH numbers should also be "taken with a grain of salt" LOL and not relied upon as absolute.

Mg "“ This is the hardest one. Test A turns color at between 26-29 drops. Test B takes either 5, 6, or 7 drops, depending on which family member I'm asking to interpret the color result (figured I'd enlist the help of a "˜second-set-of-eyes' in my measuring). This leaves me in a potential range of 950-1200 for Mg, for any given sample.

3-Do manufacturers independently publish Ca, Kh and Mg levels that their salt mixes to at a S.G. of 1.26 at 78 degrees? I've seen many posts of different people's experiences using their own test kits to measure results of different brands, often to a SG of 1.26 at 78 degrees, but do the manufacturers themselves publish this kind of data? It seems to me the industry would want this sort of stuff published and maintained pretty regularly, given that it apparently can change over time for any particular manufacturer?

4-Why would a company like Korallen-Zucht publish ranges for "œOptimum that differ from the actual parameters their own salt mixes to? water parameters" http://www.korallen-zucht.de/cms/files/zeoguide_103_english-1.pdf

I'm new to this, so if its been answered, links to the answer to these questions are very helpful. I've been searching the forums and have been reading lots of different/conflicting information and its getting confusing.

Thanks !

 

[Reefer07]

Well just a couple quick bits off hand. I think measurements really depend on how long after the salt is mixed it is tested. I.e if you test within a hr it may be higher. And if you wait a while the dkh drops with pH and such. Also from what I've read your supposed to physically mix the actual salt up, stir up the powder before mixing it with your water. This gets all the elements that have settled in the bottom of the bucket/bag.

And yes these are hobby grade test kits. There is definitely going to be a good 10% or so variation. However, this is why we are given acceptable ranges to keep our tank at. I.E. Calc. 400-440 even a little more or less. Put yourself in the middle of that number with a 10-15% deviation and your still good. I like to have a couple different test kits for the same parameter to check them against each other. Personally, one time I used a salifert Mg test and a red sea test and they both popped up at 1360 which was awesome. I'd be willing to bet my Mg was right around there.

 

[androal]

And yes these are hobby grade test kits. There is definitely going to be a good 10% or so variation. However, this is why we are given acceptable ranges to keep our tank at. I.E. Calc. 400-440 even a little more or less. Put yourself in the middle of that number with a 10-15% deviation and your still good.

Thank you,

After doing about 20 tests, I'm starting to get more of a feel for how to read the results, and I basically know where the kits are "starting" to change over, so its really only a matter of a drop or two off, once I've settled on whether its at drop 3 or drop 4 that it starts to change. Also with the Ca and Mg kits, there is a difference a few minutes later in the color. I've found it helpful, particularly with phase 2 of the Mg test kit to take my time in between drops, 4, 5, and 6.

I'm getting more comfortable with the "squishy" numbers of the hobby. I think there's a general tendency to place a higher degree of accuracy on most of these figures as can be reasonably expected to be obtained by the basic hobby-grade water test kits. My local water authority here will test any water sample I bring in and run it through an atomizer for intensely accurate numbers if I really want it. At $150/test, I doubt I'll be using their services though. Triton has a pretty good thing going at $500/year (shipping included) to run lab-grade results on a comprehensive panel of elements, run monthly - tempting...

http://uniquecorals.com/triton/trit...t-single-test-vials-with-return-shipping.html

I'm sure most of us will do just fine to be "close" to within a range of "optimal " with the hobby kits though...

I still don't understand why Korallen-Zucht recommends targets for "optimum" at:

Ca 410-430
Kh 6.5 - 7.5
Mg 1250-1300

Then manufacture salt that mixes to:

Ca 380-390
Kh 10.0-11.0
Mg 1000-1100

Unless I'm way off on the hobby kit results, that's what I get with their mix.

Trying to move the needle on Mg with dosing is like watching paint dry too I might add. It takes at least 24 hours for me to get the dose to increase my Mg by 50 points at a time. Usually it takes me 2 days to do that. So going from 1000-1300 means I'm pushing what seems like horse pill doses into my system over nearly two weeks, just to bump it up a few hundred points.

My system responds immediately to very moderate Ca and Kh dosing though...

 

[Reefer07]

Ya raise stuff in small quantities twice a day. Especially Mg because it doesnt get used up as quick. I think my tank sucks up about 60-80 Mg in two weeks.
Also, you want to read the color change right away. Any titration is gunna change colors if it sits.
And there are many articles out there that talk about proper methods to give correct/accurate results. I.e. Make sure exactly 5ml or if theres a line in the test cuvette make sure the bottom of the miniscus is at the line....etc. etc.

 

[dkeller_nc]

My guess is that KZ is publishing "optimal" numbers that correspond to natural seawater, which is typically Ca = 400 ppm, dKh = 7, Mg = 1300 ppm. I'd also guess that they manufacture the salt with the intent of putting exactly those amounts into the mix. However, when the salt mix sets around in non perfectly dry conditions, some of it reacts into non-soluble CaCO3/CaSO4, possibly entraining some magnesium in the insoluble CaCO3/CaSO4 precipitate.

But that doesn't explain the high Alkalinity, though I'll note that a lot of salt mixes initially mix up with quite a high alkalinity. It's definitely not "hobbyist test kit accuracy" issues, as the standard laboratory method for alkalinity titration is a relatively simple procedure that can be done with a pH meter, a burette, a standardized acid solution, a stir plate and a stir bar. I've compared Salifert and Red Sea's alk tests to the lab standard, and they're quite close (within 0.5 dKh).