Ditto what Teraphage said. I wouldn't look to those kinds of spirits to solve a nutrient problem. It's better to tackle the problem at it's root. I've only ever met one person that's kept (what I would term) a successful reef tank using tap water, and even that I think is still an anomoly. Tap water will contain many kinds of contaminants you don't want in your tank, so doing changes w/ tap water based SW, will not do a lot of help (you may have a net import of nutrients, if your tank's filtration is up to snuff).
I know Tom sells RO/DI, and I'd be amazed if Millie and Jon didn't as well. Walmart's got cheap filtered water in 5-gallon jugs as well. Ultimately, a home RO unit is your best solution. There really is no substitute, and IMO, you can't 'skimp' this part. Of all the things you
must have to keep a reef, this is pretty high up on the list (and mind you, you're talking to a skimmerless DSB running weird-o here, so
must is a relative term). The Tap Water Purifier is a cheap second, save your $$$ for an RO. There's folks getting out of this hobby all the time, you see folks taking down systems, and lots of folks upgrading. You can acquire what you need for less than new if needed. The RO equipment sold at the local hardware stores will work as well (while there's a difference in types of membranes, Reverse Osmosis is Reverse Osmosis)... tell the wifey you want to get one of those 'whole house' systems, so the drinking water doesn't taste funny anymore...
- Mac