I would add some ag lime. Calcium and magnesium are the major constituents in total hardness. You have 0 CA hardness "Calcium Hardness 0 ppm". "Calcium is an essential element for fish, and moderate
calcium levels in aquaculture water aid in fish osmoregulation during stressful periods. As noted above, calcium is important for egg and larvae development." Ca (calcium) -Desirable range More than 20 mg/L Acceptable range More than 5 mg/L "