To take water samples from aquariums/ponds for testing chemical water parameters, you need a non-sterile glass or plastic container (e.g. a 500 ml bottle which previously contained water).
To obtain a representative sample without any air included, collect the sample approximately in the middle of the aquarium and close the container under water.
Samples from ponds should be taken in an area of the pond with little water flow, not close to the filter and not directly underneath the surface. If possible, avoid larger pieces of dirt in the sample.
When shipping the samples, cooling is recommended.