The reef snow is nothing more than suspended phytoplankton, and will definitely contribute to high nitrates. As for the rest of the supps you are dosing a ton of different chemicals most of which that you cannot test for. Most of the supplements that you are adding can be maintained through water changes.
As for all the different planktons that you are feeding you probably do not have enough filter feeders in the tank to absorb all the extra food that you are inserting. This will lead to increased nutrients that will break down into nitrates.
This is what I would do. Stop all of the dosing. Only continue dosing for alk, calcium, and magnesium. With all of the water changes you are performing all of your parameters should be in line. I have adopted the policy that if you cannot test for a certain parameter than you should not be dosing for it. The strontium is replenished through water changes, as for iodine and potassium there are some major debates on this forum as to whether or not they are worth dosing.
Stick to the basics for a few weeks and you should see some major improvements. If you are set in stone on planktons then I would stick with one type and use a live strand of it.
Some of the best tanks around the world only dose the 3 basics.
Good Luck,