need input

[xxxgreg]

I need an idea on water changeing.
If you use tap water and then do the right thing and change to ro-di and you have 55g of water how much water do you need to change before you have all the tap water out?????

 

[scsinet]

There is no way to tell, unless you drain it all out and replace it in one big change.
I'd suggest a series of (3) 50% water changes if you were really determined to do it... but really, if your tank is doing fine, don't bother, just keep doing your regular water changes with RODI water.

 

[xxxgreg]

hay thanks, my tank is doing just fine I just want to add some corals and ive been told if I didnt have ro-di water theyed all die and I dont want to kill them .I changed 50% of my water today and just want to know when it would be safe to add more stuff

 

[scsinet]

Tap water has all kinds of crap in it that you don't want, chlorine, fluoride, metals (iron, copper, etc), all the type of stuff that can kill your corals.
I say CAN, not "definitely will." RODI is one of those things that helps you be successful and eliminates a lot of head scratching when things go wrong, from the uncertainty of what chemicals were in your source water.
If things are fine so far, I'd proceed with adding your corals, and continue to do your weekly water changes. If you want to get rid of the tap water faster, do maybe 20-30% per week for the next 4-6 weeks, that should get so much of it that the rest is negligable.