Fishless (temporary) planted tank question

Hi all,

If you read my little disaster story last week in alt.aquaria, you would
know my 40g display tank is now fishless. I don't want to restock until I
move (late Aug/early Sep), but I do have plants in that tank that I'd like
to keep healthy until I restock. The plants are Aponogeton bulbs (not sure
on the actual species as I got it at a fish auction and they were labelled
"assorted"), Crypt. wendtti "red" and java ferns. The only surviving
animals in the tank are the MTS and pond snails, so there is still an
algae control crew and substrate aeriation by the MTS.

I know the biggest concern with fishless tanks is making sure the plants
have sufficient nitrogen compounds. Well, "luckily" for me (as long as I
don't personally drink the water) my tap water has anywhere from 10-40ppm
nitrates in it. The whole reason I put plants in this tank in the first
place was to help control the levels of nitrate because of the high tap
water levels. Would weekly 10-20% water changes with this tap water be
sufficient to provide all the needed nitrogen?

Also, I currently dose with Flourish, Flourish Potassium and Flourish
Iron. I dose Flourish twice a week and Flourish Potassium and Flourish
Iron once a week (usually after the water change). The Flourish and
Flourish Iron I dose at the recommended label amounts. The Flourish
Potassium at half the recommended label amounts (crypts seem to hate the
full amount). I also inject a moderate amount of CO2 (via a Nutrafin kit),
enough to take the pH from off the high pH test kit scale (over 9.0) down
to about pH 8.4 with KH of 20 (this is a rift lake cichlid tank). I can't
remember the calculations to compute CO2 levels off pH/KH information, but
hopefully that is enough information for you guys. Should I make any
adjustments to the dosing or CO2 injection until I restock?