Use Of Rainwater For Marine Aquarium?

[phishyphil]

Hi there,

Currently considering converting to the salty side and asking loooooads of questions so apologies for the hassle

Would I be able to use rain water for my water source in my marine tank? Obviously add salt and check salinity. Would this be a viable option to cut down on the potential chemicals in tap water? We have a 3 large water buckets outside which collect rain water, would i be able to use these? as long as they having been standing for weeks.

Thanks

 

[ainsy]

NO - Marine organisms are very sensitive and you have no control over what is in the rainwater that you add. (Think acid rain!)

Also if they sit outside all kinds of muck and debris could fall in and that would lead to organic waste (Ammonia, ates and ites) that you don't want in the tank.

 

[Donya]

Well, there are two problems. One is mentioned above: acid rain. If you have buckets with water in them now, go check the pH. You can also check the other things mentioned and see whether any of them are really a problem. It is likely that it will not be perfect water primarily for the pH issue, but rather than just guess how many teeth the horse has, why not go out and actually count! Then you know exactly where you stand. Many years ago when I had a similar idea for fw tanks to avoid copper from pipes, I found that the rain water was pretty awful in my area. It was off the low end of the chart on the liquid pH test kit I used, which went down to 5.5 or something.

The other problem is volume. Even in a pretty rainy area, you'd need a pretty gigantic collection setup to accumulate any useful amount of water for a reasonably sized marine system. Given that most marine tanks require water changes every 1-2 weeks, if you have to wait through several WCs before you have a rain water WC, you really won't be making a dent in any effects the tap would be having. It would seem more viable to use rain water (if it's perfect) in place of freshwater top-ups since the volume needed per unit time should be a lot smaller, and you would potentially avoid adding lots of carbonates with each top-up (those and phosphates being the biggest problems associated with using tap water in my experience).