water testing, liquid vs strip chart
NetMax
idea that liquid reagents are generally better than strip paper tests
is correct, but the idea that liquid reagents are accurate is just not
right. Also the word accuracy needs some explanation. 'Absolute'
accuracy is what you get from test labratories using methods and
equipment which are not affordable by the average hobbyist. 'Relative'
accuracy is what you get from liquid reagent tests and this goes a long
way to meeting our requirements.
Fish are not concerned if their pH is always 7.0 or 7.5, but we would
be concerned if the pH changed from 7.5 to 7.0 or vice-versa, because
within a wide range, it's the rate of change which stresses fish, not
the absolute value. If your pH test always says the water is 7.7, it
may well be 7.2, but that's it's consistant is usually the greatest
importance.
Manufacturers do not use the same reagents (patent infringements), so
all pH testers (or anything else we want to measure) will NOT be
comparable between different manufacturers. If your AP tester says the
water is 7.2 and your TetraMin says 7.6, the question is not really
which is right (they are both wrong), but which can you see better
(color & hue) so that you can always use only one or the other.
Also because so many different re-agent recipes are in use, your water
particulars might include something which contaminates the tests. The
most obvious is ammonia tests when ammonia detoxifiers have been used
(some tests add both toxic and non-toxic forms together into a single
reading, others keep them separate). There are minerals which skew the
readings as well, though these are not well documented. Then there are
the ranges, such as Hagen's low, mid and high range pH tests. Even
though many levels are common to more than one of these testers, they
will generally give you different readings, and they have different
susceptibilities to pre-existing mineral/chemical contamination.
Then there is their readability. Looking down the tube can be great
for giving you the color, but not the intensity. Intensity is from the
side using natural indirect sunlight. Holding it against a white
background helps. Also women generally have better color accuity, so
have them double-check your readings. For titration tests such as gH
or kH, if your readings are very high, half your water sample to 2.5ml
and double your result (saves reagent).
In the trade, when we want relatively accurate reading, we cherry-pick.
Company A makes a really good high-pH tester, company B makes a fast &
accurate NO2 tester etc etc, but for the average hobbyist, relative
measurements done at the right frequency is imo, much more usefull.
So that's all the bad stuff I know about liquid reagent testing.
Generally strip paper has a few more disadvantages, but I'm not
experienced enough with it to give you the work-arounds, so I'll leave
that to others.
cheers
NetMax
Adam
Let me see if I can keep it short:
1. I don't put much faith in the readings I get from my tests (liquid
or strip, I do have more faith in my pH and TDS meter)
2. I use strips for quick snapshots, to see if things are as they were
last week
3. I use liquid reagents when I feel like something may have changed
and I want a slightly better picture of what is going on.
4. I have tested enough with both liquid and strips to have a feel
(whether it is correct or not...) for what the readings mean. I stick
to the same brands as much as possible to keep things as consistent as
possible, at least in my head.
Altum
kits that go from yellow to blue are liquid bromthymol blue (BTB), and
most high range kits are cresol red. pH indicators are in the public
domain so you're not going to find a lot of variablilty. Some kits may
have color charts that are easier to read than others, but that's about
the only difference. If you get a reading of 6.8 on one BTB kit and
7.4 on another, something is wrong with one of the kits. In fact, I
usually keep a color chart from a kit and buy the cheapest bottle of
BTB I can find.
Liquid pH indicators are actually surprisingly good. They're usually
not chemically reactive and laboratory scientists often use them as a
"reality check" for pH meters. Anyone who has ever done tissue culture
knows EXACTLY what color phenol red should be at pH 7.4! You should be
able to get reliable, reproducible readings to within 0.2 units if
you're in the range where the indicator is really changing color. The
big problem with aquarium kits is that everyone buys BTB and then tries
to read alkaline, pH 7.8 tap water with it.
Note that it's much harder to use a liquid pH kit if you're adding CO2
to the tank. Shaking the test tube to mix in the BTB drives off some
of the dissolved CO2 and shifts the pH. This is why people who run CO2
often use in-tank indicators, pH meters, or even dip strips.
--Altum
luca
Now I can say with some confidence that I am quite happy with my
cheapish AP pH test. Incomparably easier to read than the equivalent
dip strip test, IMHO. Thanks for the Interesting note on the CO2, it
may explain something... :-)
Going back to nitrates, the more I'm reading the more I am getting
confused: ppm, total Nitrogen, 4.4 multiple...? IOW, what do the
nitrate kits actually measure, and do they all measure the same thing?
Luca
Altum
luca wrote:
> Now I can say with some confidence that I am quite happy with my
> cheapish AP pH test. Incomparably easier to read than the equivalent
> dip strip test, IMHO. Thanks for the Interesting note on the CO2, it
> may explain something... :-)
I can shake a water sample from my KH6 CO2 tank and watch it go blue.
Gee-whiz chemistry. ;-)
> Going back to nitrates, the more I'm reading the more I am getting
> confused: ppm, total Nitrogen, 4.4 multiple...? IOW, what do the
> nitrate kits actually measure, and do they all measure the same thing?
See if this helps.
http://www.practicalfishkeeping.co.uk/pfk/pages/show_article.php?article_id=96
--Altum
NetMax
Altum wrote:
> Waitaminute. pH kits aren't that variable. All the aquarium liquid pH
> kits that go from yellow to blue are liquid bromthymol blue (BTB), and
> most high range kits are cresol red. pH indicators are in the public
> domain so you're not going to find a lot of variablilty. Some kits may
> have color charts that are easier to read than others, but that's about
> the only difference. If you get a reading of 6.8 on one BTB kit and
> 7.4 on another, something is wrong with one of the kits. In fact, I
> usually keep a color chart from a kit and buy the cheapest bottle of
> BTB I can find.
What you're saying makes perfect sense. Hagen using something
different for their wide range pH test? Is AP using a different
dilution for their BTB? I don't know. Try it and you will invariably
see a variation.
> Liquid pH indicators are actually surprisingly good. They're usually
> not chemically reactive and laboratory scientists often use them as a
> "reality check" for pH meters. Anyone who has ever done tissue culture
> knows EXACTLY what color phenol red should be at pH 7.4! You should be
> able to get reliable, reproducible readings to within 0.2 units if
> you're in the range where the indicator is really changing color. The
> big problem with aquarium kits is that everyone buys BTB and then tries
> to read alkaline, pH 7.8 tap water with it.
Well that's my range, 7.7 to 8.4pH. A difference of 0.3 to 0.4 was not
unusual between makes.
> Note that it's much harder to use a liquid pH kit if you're adding CO2
> to the tank. Shaking the test tube to mix in the BTB drives off some
> of the dissolved CO2 and shifts the pH. This is why people who run CO2
> often use in-tank indicators, pH meters, or even dip strips.
Hmm, thanks for that one.
NetMax
> --Altum
Altum
NetMax wrote:
> Altum wrote:
> > Waitaminute. pH kits aren't that variable. All the aquarium liquid pH
> > kits that go from yellow to blue are liquid bromthymol blue (BTB), and
> > most high range kits are cresol red. pH indicators are in the public
> > domain so you're not going to find a lot of variablilty. Some kits may
> > have color charts that are easier to read than others, but that's about
> > the only difference. If you get a reading of 6.8 on one BTB kit and
> > 7.4 on another, something is wrong with one of the kits. In fact, I
> > usually keep a color chart from a kit and buy the cheapest bottle of
> > BTB I can find.
>
> What you're saying makes perfect sense. Hagen using something
> different for their wide range pH test? Is AP using a different
> dilution for their BTB? I don't know. Try it and you will invariably
> see a variation.
Wide range kits are usually a mixture of indicators. We used to have
wide-range test strips in my lab and they weren't worth the paper they
were printed on! The only ones that were useful had a bunch of test
pads with a different indicator on each pad. You looked to see which
indicators changed and then read the pH from the single dyes.
Because of that experience, I've never even tried a wide-range kit. I
can only imagine how confusing and muddy the mix of colors must be. If
my water sample is too high for BTB, like my pH 7.8-8.0 tap water, I
usually use a cheap high-range cresol red kit like AP. If it's too low
for BTB, something really bad has happened to my tank!
I just finished reading a PFK article linked from the nitrate article I
posted for Luca that bears out your experiences with broad range kits.
They did get good results from the BTB kit.
http://www.practicalfishkeeping.co.uk/pfk/pages/show_article.php?article_id=554
> > Liquid pH indicators are actually surprisingly good. They're usually
> > not chemically reactive and laboratory scientists often use them as a
> > "reality check" for pH meters. Anyone who has ever done tissue culture
> > knows EXACTLY what color phenol red should be at pH 7.4! You should be
> > able to get reliable, reproducible readings to within 0.2 units if
> > you're in the range where the indicator is really changing color. The
> > big problem with aquarium kits is that everyone buys BTB and then tries
> > to read alkaline, pH 7.8 tap water with it.
>
> Well that's my range, 7.7 to 8.4pH. A difference of 0.3 to 0.4 was not
> unusual between makes.
There are a few different dyes used for high-range, which is probably
why you're seeing such differences. Novalek/Kordon uses phenol red for
freshwater high-range but the range of that dye is a low for your
application. It's usually done changing color by pH 8 or so. It's
best around pH 7.4, which is why it finds such wide use in biology
labs. http://www.novalek.com/kordon/aquatru/aquatru_ph.htm
Some high-range kits use m-Cresol purple, and that dye is no fun to
read at all. Is it grey? Purple? In-between? *squint* Where's my
spectrophotometer?
My favorite for your pH range is cresol red, the dye in API's "high
range" kit. It's reasonably easy to read the color change, and the kit
is cheap. Their color chart is a bit weird, but it's like BTB - once
you're used to the dye you don't even need a chart.
--Altum
Mister Gardener
named names - too often, articles like this describe everything except
the brand name. And most of us would prefer to skip the technical stuff
and get straight to the "what brand is best so I can buy it."
I was, however, quite disappointed to find that they made no mention of
what has to be one of the most common kits available, API's reagent
test. API's DryTab test did very well - but that tells me nothing about
the dropper version. The photo at the top of the article appears to me
to be identical to my API reagents color card. I've been skeptical
about tests using dry tablets or powders because of my fear that my
sloppy storage methods or handling might accidently get the stuff all
wet and ruin the kit. Ease of storage and use is my number one, well,
number two at least, concern. I'm going to take another look at API's
DryTabs. (Long pause while I scramble to several web sites and check
for hits on Google.) OK. I've looked for them. Unavailable at That,
Al's, Doctors, Petco and Pet Solutions. Visited API's site. No mention
of the Nitrate Dry Tab at either the North America or UK site. A Google
search shows Dry Tab test kits available at Internet retailers in the
UK. What am I missing?
MG
luca
I read the article, and it answered several questions, thanks for
linking it. I'm not positive on which test had the best results in the
end, the Seachem one? Also surprised to see so many tests performed so
poorly, even the Salifert one didn't do well... Is 'readibility' the
Achille's heel of nitrate tests?
Luca
NetMax
Altum wrote:
...PFK article ... bears out your experiences with broad range kits.
cancel out the:
Altun wrote:
Waitaminute. pH kits aren't that variable
for a general topic including all the pH test kits? :p
NetMax ;~)
Altum
read at 40 ppm when better kits read 15 ppm. Seems like I remember
someone on rafm a while back that was having the same problem with the
API liquid.
I'm using Seachem now and if it's too pink to read easily, I dilute the
sample. To be honest, I hardly ever test anything but pH when the tanks
look good. I just fertilize with my powdered EI mix until the plants
pearl. ;-)
--Altum
Altum
OK, so I learned someting from the PFK article. :p I didn't realize
how lucky I've been sticking to API's cheap, one-indicator test kits!
*grin*
--Altum
Mister Gardener
MG
Tommy Butler
--
Tommy Butler
Gill Passman
Tommy Butler wrote:
> Maybe if you ask Gill really nice and say something like "america sucks"
> then she'll go get you a pack from her UK LFS and send it to you.
>
Wasn't going to rise but I will....I have never once said I believe
"america sucks" although I might be a little guilty of playing that
international game of "Bait the American" from time to time.....bit of
like the French playing the "Bait the Anglais" and indeed the USA game
of "Bait the Canadian" (and yes I do know it goes on).....and indeed
the American game of "bait the Brits) - we all do it and it is without
malice (at least not from me)....
On-topic I've never seen the stuff on sale - I use the Nutrafin test
kits (liquid) for Freshwater and the Red Sea stuff (again liquid) for
Marine.....
Gill (about to drop Tommy a pm)
Tommy Butler
--
Tommy Butler
Tommy Butler
--
Tommy Butler, thinking of lab equipment test kits
Gill Passman
I didn’t call your continent a turd….I just asked out of curiousity what the turd appearing out of the clouds was….I had no idea it was NA when I asked….OK – got my mail yet?
Gill
Shitty
Where can I get these strips charts or the liquid from?
denizen
Shitty wrote:
> Where can I get these strips charts or the liquid from?
Your local aquarium fish store, or an on-line supplier like Big Al.
With that nym you must keep goldfish, eh?
d.