Where to throw away water hardness tests?

Question

I was recently at a relative's house where we tested the hardness of the water. The testing kit contained two bottles A and B. Addition of one drop of A followed by addition of drops of B until colour change determined the hardness. One drop of each were required in 5 mL of water.

I didn't take a photo of the composition as it only provided the empirical formula of the various compounds, but it was complex (more than 6 molecules) and toxic to aquatic environments as symbolized by the pictogram below. There were no indications on what to do with the 5 mL of water after testing.

I was therefore wondering how to dispose of the solution. I have no idea whether A and B actually neutralize each other to produce something non-toxic to aquatic life, or at what concentrations they are actually toxic to aquatic life. Nevertheless, I assume it would probably be better if we didn't just throw random toxic chemicals down the sink or in our gardens.

I am therefore open to suggestions or opinions on how to deal with such a situation. Note that I am aware you can buy strips, but the liquid testing kit was already present.

Thank you

Answer 1

For the total hardness, there is probably ammonia pH buffer, EDTA and Eriochrome Black T as complexometric indicator. The former two are harmless enough when diluted by water and the indicator is already very diluted when used, not speaking about dilution at disposal.

Similarly a diluted acid with pH indicator (probably methyl orange) for the carbonate/temporary hardness. Dilution at water sink disposal is enough.

I remember some aquarium test kit involving exactly this.

Most of home cleaners are more nasty than these two sets.