Just a quick update.
Water parameters:
NH4: 0
NO2: 0.05
NO3: 10
Fe: 0.4
PO4: 1.5
K: 20
PH: 6.85
Temp: 78F / 25.5C
Tank size 30g, filter Eheim prof. 4 600,
Feeding fish twice a day. No change in diet. CO2 injection. Lights on 11 hours a day.
Fish was eating happily this morning.
Also I do 50% water changes every week.