Nursery Water For Top-offs
 

I checked the website for this product and it states that the water is filtered through sand and activated carbon to remove chlorine and other impurities, then distilled using stainless steel pipes (not copper), then treated with ozone, and that minerals calcium chloride, potassium chloride, and magnesium chloride are added for taste. Any thoughts or opinions on using this water for top-offs?

If you are measuring calcium and magnesium, there wouldn’t be an issue with accidently overdosing these ions by using this water. No opinion about potassium. I would guess that the level of chloride in the water is too small to worry about.

I agree that the levels of ions from the minerals likely would be too small to be of interest. I would treat the water with something like Prime or the like that had metal and ammonia binders and could deal with chloramine and chlorine. The filtered water might be safe enough if the setup is maintained very carefully, but they don't have any need to remove all the chlorine or ammonia for their product, so they might not worry too much about those levels.

I would be concerned that Fluoride is added to that water.

(And what justifies them to add Fluoride to toothless infant's water is beyond me?)

I wouldn't worry too much about fluoride in saltwater. The ionic level already is very high, which makes a difference. Toxic levels for marine animals seems fairly high, from what I can tell. I'd probably still use RO/DI, out of general caution, but a regular water change schedule can help with a lot of problems.

The Nursery Water comes in two varieties, one with fluoride and one without. I'm using the non-fluoride type out of caution. The only reason I went this water is because my local stores often run out of bottled distilled water that I regularly use without any problems. (I think people use distilled water for other reasons, such as home-brewing beer, a big thing here in the Northwest.) So, I won't be using the Nursery Water on a regular basis, just when the store is out of stock of distilled water. (I know RO/DI is the best.)

That sounds like a good solution to me. :)