Ok so no more feeding snails.
I am in north-west melbourne. I don't have any way to measure KH at the moment.
I am skeptical of the result I got from the laundry being so different from the other taps, I'll leave some water out for a while and test again. I feel you may be right about the CO2.
-16L Planted tank, cherry shrimp and a mystery snail.
-10L live and silk plants, Finn plakat betta.