Rain barrel water safe to top off mini ponds?

[WillMcK]

Is it safe to top off my outdoor mini ponds with collected rainwater from a rain barrel? I've read conflicting advice on the internet about rainwater having a dangerously low pH. But what about when it rains? If you top off with a hose, then is it okay to top off then immediately dose prime?

[Eric R]

It seems to me that a lot of people allow their ponds to naturally top off with rain water, if they aren't under cover, and just have some sort of overflow installed so that the pond doesn't overflow its edges if the water gets too high. If you're worried about ph, you can periodically check your pond kh levels and mix in a bit of baking soda or a small bag of crushed coral to add carbonate buffer to keep your ph stable.

If your pond is covered such that you need to manually top off, rain water should be fine, as long as your rain water collection container and your roof don't leech anything into the water. This can be a problem if you have an asphalt shingle roof instead of a metal roof.