Ahh yes, I see that now... Found this little tidbit, should have just stopped to think about it for a moment! The answer was in the name... ha!
Deionized water, however, is inherently acidic
and contaminants such as copper, dust, stainless and carbon steel and many other common materials rapidly supply ions thus re-ionizing deionized water. The very lack of ions make deionized water unusually corrosive and one of the most aggressive solvents known
So unless I want to clean my fish really well huh