i use kent and i find im still a little off on my ph . if im topping up the tanks water the straght ro water sends my ph for a loop.

Off topic a bit, but I had pH problems for a while also. I tossed my pH meter and haven't had a problem since!! :razz:
When your pH went for a "loop", what exactly happened? went high? Low? Were you measuring the RO water itself? If so, that will be loopy for sure. It's difficult to get a true reading for pH in RO water.
I've been using RO for a couple of years and have never felt that it needed any additional things added.

If you can throw in a bypass valve befor the membrain I would just use the filtered water for your fresh water, as mentioned RO water is to pure for fresh water tanks and you should use some sort of remineralizer befor you use it. as for salt water the salt mix is the reminerializer.

Steve

I see.. I guess I can do that too. Wouldn't be too hard since I have some extra tubing and a valve. I will have to give it a try.

Thanks

IMO your plain tap water (dechlorinated) is fine for most fw fish, aged tap water for more sensitive fw fish.

Agree with the pro-tap water crowd. Lower mainland Vancouver water is fairly soft as is. I wouldn't even bother with RO for top off. Unless you are using a pH buffer or using a buffering substrate FW tanks can benefit from the slight hardness reintroduced from top and water changes from the tap. Otherwise buffering capacity can eventually get exhausted and the pH can plummet.