My use of Purple M in my new system dosed at half recommended dosage for a low nutrient system (5ml for 100g) created different results.
Prior to dosing I was reading Nitrates around 20ppm and Phosphate at .127
The week after dosing Nitrates struggled to stay above 5ppm without manually dosing 5ml of NeoNitro every other day. Phosphate lowest was .028ppm after 1 week which during this time I had manually dosed 5ml of NeoPhos twice, and the last 4 days before lowest result I had been dosing phos-feed during the night at 1ml phos-feed per night.
I am 11 days since using Purple M and finally starting to see my Nitrate and Phosphate level out and slowly increase.
Interesting that you report such significant change in Nitrates and phosphates. Also, not sure why the nutrients would start rising again if you are consistently dosing the same. You mentioned this is a new tank. Not sure how new. Days, weeks, months? There's a lot going in in the beginning with the biome. Also, if its a new tank you might be still adding, changing, etc. To do a good test you need NO variables other than the new product you are using. Otherwise, you can't be certain what is causing it.
In my case I made sure to do the testing over the course of almost 2 months with three different products. Water changes, feeding, lighting, trace element dosing was all the same. NO other bacteria products used at the same time. Testing was done daily with a Hanna ULR Phosphate tester and Hanna Nitrate tester.
Make sure your environment is stable and nothing else is changing and maybe try the testing again for at least 7 days straight with no other changes. Honestly, I can't reconcile in my mind how a tiny 5ml (cap full) of this product would cause all those nutrients to be consumed so fast. No bacterial bloom occurred?
Good luck and let us know if these results are repeatable.