Weird Salifert test results

[Pennywise the Clown]

A month ago I replaced my Salifert test kit. My last reading with the old kit was around 420 if I remember correctly. The new test kit gave me a reading of 480.
Today I replaced my Salifert Magnesium kit which was reading 1300 and the new kit is reading 1500!!!!
What's going on?

 

[Quietman]

Replaced Salifert with Salifert? Those readings are both about 10% variance. Many possible explanations. Hobby grade test kits are reasonably accurate but not lab grade. Although I find they are usually consistent within the same batch read by same person.

Could be older chemicals, opening reactive chemicals to air could impact readings just with normal use. Different batches. Paying more attention to readings and procedure due to new box. Could be a bad batch in previous or replacement. Could be cumulative errors or tolerance of 5% each.

 

[Larry L]

Were the old kits expired? Also check that the test kit instructions are the same - the last time I got a new Salifert Magnesium test kit I noticed that the instructions are slightly different (no need to swirl for 30 seconds after adding Mg-1).

 

[Cory]

1.135 grams of baking soda in 1 gallon of pure water is 10dkh. Check your salifert test kit!

 

[Quietman]

There's also saltwater standards on BRS website from Fauna Marin - Covers all the majors. Bit pricey - $20 for 100 ml.

 

[Graffiti Spot]

Lots of the kits changed the amount of drops you use as well.