That's the interesting part, I've never been able to get a positive reading for phosphate at all in my tank - I think I'm using my Hanna meter correctly, but I'm probably going to make a phosphate standard and test it to make sure it's working (and I'm using it) as it should. I do need to test out of my tap though, just haven't done it yet.
@anathema - I want people to pull rank on me, that's why I'm asking questions - and will continue to, probably to the point of annoyance
. I appreciate the response, I've received more feedback and discussion than I anticipated, and that's awesome. One thing that's fun/tricky about this is there seems to be as many ways to do things as there are tanks, so I try to ask folks what they're doing and extrapolate to where I'm trying to go to hopefully minimize my chances of doing something stupid. What you wrote is very useful, and I thank you for it.
@bluprntguy, that's exactly what I was thinking; if phosphates are measurable out of the tap, treat with GFO before adding it to the tank. Glad to hear folks have done similar things.
So at this point, I'm going to seriously consider a slow, carefully observed switch over to tap after installing a filter and doing as much testing of my tap water as I can. I'll be sure to post thoughts and observations for those who are interested. And please, I'd love to hear any additional insights or experiences!