Expired test kits

[Treebeard]

I just realized that my Salifert PO4 and NO3 test kits were past their expiry dates, like 3 years past. Does anyone know what happens to the accuracy of these kits as they age? Do they tend to test high or low?

Since I need to replace them also wondering if I should switch to Elos.

[mrhasan]

I just realized that my Salifert PO4 and NO3 test kits were past their expiry dates, like 3 years past. Does anyone know what happens to the accuracy of these kits as they age? Do they tend to test high or low?

Since I need to replace them also wondering if I should switch to Elos.

Chemically, they should read low. But depends on the compounds present in the tests and might test high too.