Matching up the fluid in the test vial to the color card

[Tomorleans]

when you're usuing the test kits with the glass vial and you're matching up the color in the vial to the color card do you hold the vial against the white background or off of the background slightly.. Cause that's a difference of 40ppm nitrates or 20..

[Reefmack]

It depends on the maker of your test. I use API kits for my freshwater tanks, and I questioned API a while ago on the method of comparing the result vs. the color card. They replied to hold the vial right up against the white edge of the card.

Other test makers recommend different ways of how to view the test sample vs the card, and it's usually clearly stated in their instructions, but it isn't made clear in the API instructions.

[cdangel0]

Depends on what type of test kit you are using -some say to put the vile against the card, others to hold it 2 inches from the card, while others you have to look down through the tube while holding it against the card.

[Tomorleans]

damn.. I dont have the kit here at work. It's at home.. I'll recheck the instructions when I get home.. btw it's a cloudy day in the ocean at my house today..;) No sun for you..

[Aquarist007]

My wife claims I am colour blind--LOL

When in doubt I cover the test paper colour with the test vial--if you can't see the test paper colour through the vial then it is a match

[Tomorleans]

haha... When I go outside in the bright direct sunlight it totally changes things up a bit.. So Im outside running around the yard looking for acceptable light..

[Reefmack]

Another problem with the color cards and the solutions is "metamerism" - when 2 colors being compared look different under different light sources. I managed a color matching lab (paper industry) for years, and for example you might match the color of your standard under fluorescent light, and then look at it under incandescent light and they aren't even close. same thing as when you buy clothes in a store that seem to go well together, then you go out in daylight & they look totally different. I saw this recently with a Red Sea saltwater pH kit - under my kitchen incandescent light it looked like pH 8.0, if I walked outside in indirect sunlight it looked like 8.6. It's because the color cards use insoluble pigments to print the colors, and the solution test colors are essentially forming a water soluble dye, and if you had a way to see the spectral reflectance curves of the two, you'd see that they're quite a bit different. In my lab it was difficult or most often impossible to match a standard made with pigments, with a formula that used dyes. Too much metamerism to get a match under all light sources. Anyway, now that I've bored you with the technical junk I think the color cards pose some real issues because of this situation. But, I can't afford to buy expensive meters to measure everything, so I do the best I can. But it sure can drive a person crazy with the color cards.

[Tomorleans]

<a href=showthread.php?s=&postid=9960852#post9960852 target=_blank>Originally posted</a> by tlmack
But, I can't afford to buy expensive meters to measure everything, so I do the best I can. But it sure can drive a person crazy with the color cards.

I just got into this world of reefing and it's already an issue..

[Aquarist007]

but---you can buy more accurate test kits reasonalby: I use kits that involve adding drops of one chemical to another that perform one colour change--not a comparison. I use them for nitrates, calcium , magnesium and alkalinity.
you don't have to get too stressed out about pH anyway--it should stay relatively stable.

[TomRep]

capn- which kit uses a color change for nitrate? Just wondering cause I'm looking at getting a new NO3 kit soon. Thanks!
Tom

[Reefmack]

Yep - a lot of my SW test kits are also titration based, and while not as easy as a color card they're a lot easier to determine a result. I agree - it eliminates the hassle of trying to compare colors.