So sorry you are having these issues! Since you had no ammonia after flooding, I'm going to assume your bacterial culture grew well during the DSM stage. Amazonia is very ammonia rich (part of the process they use), so that is probably converting quickly to NO3.
Some melting is to be expected when doing DSM and then flooding, but the extent depends on the plants. The amount in the photos does look like too much to me though.
Do you know more about your water parameters such as GH (Ca and Mg)/KH, and other nutrients? Are you using tap or RO?
Personally, I would do a 75% water change to bring NO3 down, then dose based on PPS or EI levels (whatever you are comfortable with) for a week, then do one more 75% water change, dose normally and then do the 50% water changes from there on out.
The large water changes over time are really to help remove dissolved organic content as well as keep an upper limit on parameters.
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