To raise phosphate (PO4) levels by 1 ppm in 1 liter of water using 45% phosphoric acid, calculations indicate that approximately 0.67 ml is needed. This is based on the understanding that 1 ppm corresponds to 1/1000 ml, and adjustments are made for the concentration of the acid. For larger volumes, such as a 300-liter tank, the amount required would be proportionately higher, but the calculations initially suggested a miscalculation of 7.2 ml instead of the correct 0.67 ml. It is emphasized that the phosphoric acid should be added slowly to avoid high local concentrations that could harm fish. Additionally, comparisons are made to the phosphoric acid content in common beverages, highlighting the importance of careful measurement and administration when dealing with aquatic environments.