My tap water has Phosphates added to reduce pipe corosion and also has
nitrates due to the source being river and organics leach into the
water. I was having green water problems, the tests showed no amonia
and moderate nitrate (of course due to source). I found that the green
water problems occured when I used stress coat or novaqua or tetra
start right(?) to remove chlorine (The town does not add Cloramaines
(Chlorine-amonia mix)) . It seems that the product that contain aloe
type slime additives would cause this. I just use Amquel or Amquel 2
(removes nitrates or so the product claims) and have not had the green
water. I don't know why this is. I just have not had the green water
problem since.

I also visited the water treatment plant in my town and spoke to them
about the water. This was very enlightening. I found out about the
water harness and nitrates and phosphates. They showed me the
equipment they test with and what the do to the water (settling,
filtering, chlorine, and pH stabilizers). I recomend setting up a tour
of your municpal water supply department.

I do know that some test kits test nitrates/nitrites and amonia with
different reagents than others. Try different test kits to see what
you come up with.

I add iron to my water and this has been the trick for my crypts and
amazons. I have regular agate gravel so I do not know about those
"planted aquarium" substrates.