Dom, They say rain water is most polluted at the beginning of the rain, after that not that bad. I dunno why but my fish and plants seem to do better ever since I put in rain water, even the duckweed began to clear up. Miraculous stuff rainwater. Got most of my fish to spawn. Not to mention save a lot on water bill and no need to dechlorinate. Only thing is it didn't seem to work for my shrimp. I think there is a higher chance for tap water to be polluted by heavy metals than rain water. Rain water just have the risk of being too acidic or contain too much sulphur. But most of my fish south american, they look pretty happy in rainwater.

Nano, the shrimp turn white even before they die. After dying they turn red. My tigers slowly dissapeared... I saw one died by being sucked into the filter intake in my community tank. :/