Ro di...why not ionize

[mrwizard421]

Was just thinking about buying a Ro-Di filter but in research found that there are ionizers. My question is why do we deionize Water to later dose it too the level desired? If ionization creates new calcium and alkalinity levels.. Thanks for any input

 

[Randy Holmes-Farley Verified Community Expert]

We remove all ions (and many neutral molecules as well) from the water because there's no way to selectively remove the ones we do not want and keep those that we do want.

The ones we do not typically want include ammonia, phosphate, silicate, nitrate, copper, lead, pesticides, chlorine, chloramine, etc.

I discuss what is in tap water that is a worry here:

Aquarium Chemistry: Tap Water in Reef Aquaria ? Advanced Aquarist | Aquarist Magazine and Blog
http://www.advancedaquarist.com/issues/jan2004/chem.htm

and I discuss exactly how an RO/DI removes them here:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2005-05/rhf/index.htm