Testing my test kits.

Ishy · May 24, 2016

I've just gone through my test kits and checked them with Fauna Marin reference solution. The readings I got are below.

MAG should be 1315, with ref solution 1260.
KH should be 6.6, with ref solution 7.1.
Nitrate Should be 10, with ref solution 10.
Calcium Should be 422, with ref solution 405
All above Salifert.
Elos.
Phosphate Should be .2, with ref solution .2
As you can see and as I suspected some kits are way off. My question is, for future tests do I simply add the number difference, ie add 55 to the mag reading or should I take the difference as a percentage error and add that percentage to every test?
Thank's, Ishy.

glb · May 24, 2016

Ishy said:
I've just gone through my test kits and checked them with Fauna Marin reference solution. The readings I got are below.

MAG should be 1315, with ref solution 1260.
KH should be 6.6, with ref solution 7.1.
Nitrate Should be 10, with ref solution 10.
Calcium Should be 422, with ref solution 405
All above Salifert.
Elos.
Phosphate Should be .2, with ref solution .2
As you can see and as I suspected some kits are way off. My question is, for future tests do I simply add the number difference, ie add 55 to the mag reading or should I take the difference as a percentage error and add that percentage to every test?
Thank's, Ishy.

Are any of your tests expired?

Sabellafella · May 24, 2016

Ishy said:
I've just gone through my test kits and checked them with Fauna Marin reference solution. The readings I got are below.

MAG should be 1315, with ref solution 1260.
KH should be 6.6, with ref solution 7.1.
Nitrate Should be 10, with ref solution 10.
Calcium Should be 422, with ref solution 405
All above Salifert.
Elos.
Phosphate Should be .2, with ref solution .2
As you can see and as I suspected some kits are way off. My question is, for future tests do I simply add the number difference, ie add 55 to the mag reading or should I take the difference as a percentage error and add that percentage to every test?
Thank's, Ishy.

Wow thats a jump, i accually use 2 different test kits for alk and calc. Also use 2 little fishes accurasea for reference

Ishy · May 24, 2016

None of the kits are even close to expiring.

ksc · May 24, 2016

Always assume your test kits are within about 10%-20% of the actual number you're testing for. You could also assume that the reference solution is off a bit too.

Ishy · May 24, 2016

Yes, I realise that but I would like to think the reference solution is more accurate than my test kits.

morpheas · May 24, 2016

The calcium, alkalinity and magnesium test that are off are within a ~5% of their total scale which is not bad for a hobby grade kit (your eyes, the drops, the amount of water etc). I can't find their specs for accuracy but I would suspect they're around that region. The only way to get better results is to use lab grade equipment/methods (for instance triton).

You cannot add the error of the test kit because it's a +-. You have to accept that the kit will bring you within a certain range. The best you can do is what @Sabellafella said which is use multiple kits and do multiple tests to get a more average/statistically closer to true number.

Sabellafella · May 24, 2016

morpheas said:
The calcium, alkalinity and magnesium test that are off are within a ~5% of their total scale which is not bad for a hobby grade kit (your eyes, the drops, the amount of water etc). I can't find their specs for accuracy but I would suspect they're around that region. The only way to get better results is to use lab grade equipment/methods (for instance triton).

You cannot add the error of the test kit because it's a +-. You have to accept that the kit will bring you within a certain range. The best you can do is what @Sabellafella said which is use multiple kits and do multiple tests to get a more average/statistically closer to true number.

Its acually alot worse then it is, i collect test kits and theyres not one (other then "some" doubles that test the same). I acually posted some test results on my buildthread, and they all were different by a very large amount. I sent a sample to triton so im awaiting results still.

Ishy · May 25, 2016

Anyone have any thoughts on this? I'm thinking that my mag for example is about 4.5% low so if I add 4.5% to all future mag tests with this kit I should be closer to a real figure? The KH reading is around 7% high.