Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Chloramines are rarely more than about 2 ppm, so, no, massive water changes with water that has chloramines will not result in rising nitrates like you are describing.
If the tap water has 5 pppm, and the chloramines contribute 1-2 ppm, then a 100% water change should show no more than 10 ppm or a bit lighter color.
Here is what I have seen a few times:
There is some source of nitrates in the substrate.
When I do a carefully measured water change (whatever that means) of 50% I would expect the NO3 to be cut in half. But it is not, quite.
When I do the same volume of water change, but take the water from the substrate (such as a gravel vac, or a more complex method with a planted tank) then I do see the NO3 cut in half.
I still do not think this is the only cause of such quickly rising NO3, but you might start by trying this:
Dig a corner out down to the bottom of the tank and take the water change water from there, hopefully pulling it through the substrate rather than from the water column. If you can dig more holes and take water from several locations this would help.
Have you added any fertilizer tablets that might be escaping from the substrate?