No sense of accuracy in test kits.

[chasekwe]

Hi folks,


So I've purchased everything I need to start dosing 2-part and intended to get going with that today.

I feel pretty nervous about my testing though, the "drip til color change" method just doesn't give me any feeling of accuracy... it really makes me pretty nervous to get going.


So today I had my LFS test my parameters and I did it myself.

Calcium:
Me : 380
LFS : 400

May not seem like a huge difference but it represents almost ~7 fl oz difference in solution added.

Magnesium:
Me : 1230
LFS : 1200

Not bad.

Alkalinity:
Me : 8.3
Me (Hanna checker) : 7.4
LFS : 6.0

So basically all 3 of these numbers are completely useless to me. I could test again but the tests have already proven at least 2 of them are completely wrong. What am I suppose to do with this?

My test kits are salifert, I don't know what the LFS uses.

[AmberL]

I know what you mean! I did my first Alk, Mag, and Cal tests last night. It's hard to know when the color is the exact same as on the card. It's kind of frustrating. I have the Red Sea test kits.

[thegrun]

It should be noted the drop method reads when the solution turns completely to the new color, not when the color begins to change. I would trust the Hanna meter providing you calibrated it which is essencial.

[Chris27]

Suggestion - use the test kits to verify how stable your parameters are vs. a one time measurement....you'll sleep better at night and not pull your hair out chasing 20 ppm mag or calcium.

All the kits have a margin of error, just the way of it. If all the kits we use were as accurate as some folks would like them to be, they would be $1000's of dollars vs. the $30 we pay for them now.

FWIW - a 20 ppm difference in calcium is nothing when you take into account that it's next to impossible to know exactly how much water is in your tank....unless you filled your tank with un-opened 1 Gal Jugs.

[RedM3]

Your LFS tested your pH to be 6.0? I'm guessing your tank is already at least partially stocked? If so, I wouldn't believe the test results. I'm pretty sure a 6.0 pH would kill off nearly any of the saltwater fish you put in there...

[Chris27]

Originally Posted by thegrun

It should be noted the drop method reads when the solution turns completely to the new color, not when the color begins to change. I would trust the Hanna meter providing you calibrated it which is essencial.

Not always the best idea to trust the digital gauge.....user error is greatly increased when compared to a titration.

Figure it this way, for a titration you use a bit of sample measured with medically calibrated syringes, then you drop some titrant in there slowly, waiting for a change.

For a digital meter, one must ensure all the reagent goes into a curvette that must be completely clean....which is hard to do without an acid bath of sorts, coupled with completely pure compressed gas to dry it or some expensive lint free wipes at a minimum. Also, there are electronics and firmware in the meter which can go to hell quickly as well.

[The Velvet Sea]

In my opinion, the new hanna alkalinity colormeter with liquid reagents is great. I feel that there is much less potential for tester generated noise than a typical alkalinity titration kit. I can get reproducible results from the hanna within 1 ppm of alkalinity. Titration kits don't even have that degree of resolution.

[Sk8r]

Keep your vials clean: wipe out and dry between uses. Don't ever allow water to evaporate in testing tubes or squeeze bottles. If you think you screwed a count, just rinse, wipe dry and start over.

Actually this process is quite easy---as your drops hit the solution, they will not cause a color change---until they get close to the mark. then you may see a 'flash' of the color, as, for instance, the momentary appearance of bright pink that vanishes into the dark solution. this signals you are getting close, and many experienced [and lazy] testers wait til the 'flash' before going super-careful. once you see the flash, slow down and be meticulous until you see the full-blown color. if you think you've got it, add a couple more drops to be sure, but count the drops *at the time it went pure color*. Also, be sure not to read the syringe upside down. read all instructions.

testing gets a lot faster with experience; I can run the whole alk/cal/mg thing in about 5 minutes. A novice may take half an hour in the same operation. give yourself a few months of practice and you'll be perfectly confident.

also circle the expiration date on your tests, maybe even log them in your compute calendar. they're that important. if you base additives to your tank on a mistaken reading you can go wayyyyyyyyyyyyy off.

if you EVER get a bozo reading on a test, before you rush and dump something irrevocable into your tank---take a sample to your lfs and ask if they read the same.

[chasekwe]

Thanks guys,

I just checked my alk 3 more times and got 8.3/8.6/8.3 and I tested the calibration solution sent and got 7.4 spot on, which is what it should be. This is on the salifert test.

I'll mess with the hanna more later but keeping the vial ultra-clean always has me doubting myself. I'm not particularly fond of my hanna alk or phosphate checkers as a result.

[Chris27]

Originally Posted by chasekwe

Thanks guys,

I just checked my alk 3 more times and got 8.3/8.6/8.3 and I tested the calibration solution sent and got 7.4 spot on, which is what it should be. This is on the salifert test.

I'll mess with the hanna more later but keeping the vial ultra-clean always has me doubting myself. I'm not particularly fond of my hanna alk or phosphate checkers as a result.

Get yourself some Kimwipes, DI water and a little vinegar, keeping them clean isn't all that hard.....

http://www.kcprofessional.com/us/KCP...ch-science.asp