Rainwater is generally ok except during haze period. During haze period, the water is probably contaminated to the point of being acidic. Many bros here esp those with outdoor ponds noticed fish behaving odd during hazy months.
Suggest treating rainwater with baking soda to bring the KH up. Rainwater is inherently 0 KH/GH, and can result in pH swings when using it to change large quantities of water.
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