why RO water


I know this has probably been asked so many times before, but I am a little confused with this RO water "v" tap water.
I was told before I even got my 200lt tank that tap water would be ok as long as I tested it before use and all was ok.

I have now just been to me LFS and been told I should not be using tap water at all at it kills the fish. I am lucky in the sense I have no fish in my tank yet as I have only just started and was about to add the live rock and sand. However now I am wondering if I need to do a complete water change using RO water???

Your help with this will be muchly appreciated.


I was about to give you a good explanation of how tap water is fine under certain conditions but then I noticed that your question refers to saltwater tanks. I, along with many others here, use tap water for our freshwater tanks. Sorry, I have no experience with Saltwater but hopefully someone else here can help you with that.


its ok to use tap water if you carfull but I would recommend against that. get an ro system they are so much better. and don't worrie about 100% water change just do your regular scedual and it will be fine.


When I brought my tank I could only used. I could only carry 60 gallons of the orginal water (or water). So I had to use almost 80 to 90 gallons of tap water.
I didn't loose a thing and it all seemed fine.

I did start making water changes with or water.

IMO you get much better water with or and you know what you have. Your tap may have metals or chemicals in it that will harm your tank or promote alge growth.

I think you would have one less thing to worry about with or.

I would not worry about the tap that's in your tank now, but I would do your regular water changes with or water.
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