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Testing for EI

Hi all,
Way back when (even predating the "Barr Report" ..... who else remembers TB hanging about on the APD mailing list, asking loads of questions, then contributing to discussions, then dominating discussions, then finally setting up his own "pay up front" website ;) ) actual.weights of the compounds were used such that concentrations of stock solutions were known - so if you wanted 5ppm X in the water column, it was easy to calculate the volume of compound X stock solution needed.
I first heard of Tom when he was posting on Dwarf Cichlid site <"the Krib">.
I was running a million phosphate (& other) assays back then & sceptical of the quality of aquarium trade kits & had access to analytical equipment & various reagents, so amused myself with standard curves & such .... & found those test kits weren't half bad - not 3.62 ppm nitrate accurate, but 5, 10, 20 ppm, & dilute your 20ppm sample by a factor of 4 & measure 5ppm well enough. Test strip reagent pad chemistry also yields pretty decent data - IF handled & stored appropriately (& one got the brand right)
I think this is back to the real issue, it is just down to probability. If @alto you tell me that there is "x mg/l of K" in the tank water I will believe it, because he understands the scientific method, is familiar with dilution and standard curves and there is a very high probability that it is an accurate reading.

If some-one else tells me, then I'll less sure they are right, and "less sure" is the important bit.
I read a lot of anti-kit dogma on forums, but very few details of how these kits "failed" :confused:
or what the supposed interfering compounds are :wideyed:(
When I started all this I was pretty confident that I could find analyical techniques that were consistent, reliable and available to every-one, but now I really don't think that you can quantify aquarium water using the tests available to us. As an example of this since I started I've begun to realise how important humic compounds are in regulating both availability and toxicity of micro-elements, something that I hadn't really been aware of before.

I think there are two really large issues with nutrient testing:
  1. The first is that getting levels for important ions, like NO3- and K+, where nearly all the compounds they form are soluble, meaning that you have find one that isn't (potassium tetraphenylborate etc.). You can get very easily get accurate potassium (K) readings with a flame photometer or an ion selective electrode (with ISE you have to compensate for high Na+ levels), but only if you access to them. Nitrate is problematic, by any method, over the whole range of water conditions that a fresh water aquarist might experience. If you use cadmium reduction (to convert NO3- to NO2-) you have to shake the sample consistently, if you use an ISE you have to take into account interference from chloride (Cl-) ions etc.
  2. The second is that many micro-element issues relate to ratios of ions, rather than just amounts.
( & there's an amusing faith in pH values even when the measuring probes have had no maintenance or calibrations done :) )
I agree, pH probes are high maintenance bits of kit, and pH readings themselves, even if accurate, are only really useful if you know the carbonate hardness of the sample.

My suspicion would be that pH measurements show a similar level of inaccuracy to nitrate measurements, some will be OK, some won't, but it is back to probability, how do you know which readings are accurate?
I don't test anymore - but that's just because I'm lazy :oops: - I also just grab a bottle of Tropica's finest when I want to "feed" my plants
I tend towards sensitive fish (mostly wild caught) & (in)bred pretty shrimp lines, so I run my tanks lean with moderate CO2 & lighting
I do occasionally dip a strip reagent stick just to confirm that my tap water is still pretty much the same as my tank water
That is what I do as well, and my suspicion is that is what most long term fish keepers do.

cheers Darrel
 
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