Ferric vs. Ferrous Sulphate: Key Differences, Uses & Safety Guide
Ferric sulphate is the oxidised, Fe³⁺ form; ferrous sulphate is the reduced, Fe²⁺ form. The spelling “sulphate” is correct in British English; “sulfate” is the US variant.
People grab either bag when treating anaemia or clearing cloudy pool water, assuming iron is iron. Yet one tablet can stain teeth, while the other shocks algae. The confusion usually surfaces at the pharmacy or garden centre, not in textbooks.
Key Differences
Ferric (Fe³⁺) needs an extra metabolic step to be absorbed, so it’s harsher on the gut and stains more. Ferrous (Fe²⁺) is the body-ready form, gentler, but oxidises quickly. Dosage differs: 200 mg ferrous ≈ 65 mg elemental iron, while ferric preparations list the full compound weight.
Which One Should You Choose?
For iron-deficiency anaemia, choose ferrous sulphate tablets; they’re cheaper and better absorbed. For water treatment, coagulant ferric sulphate binds phosphates and solids faster. Always match the form to the job, not the name.
Can I switch between the two for anaemia?
No. Ferric salts are poorly absorbed and can worsen stomach upset. Stick with ferrous unless your doctor specifies otherwise.
Why does ferrous sulphate turn brown?
It oxidises to ferric when exposed to air and moisture, losing potency. Keep the lid tight and store it cool and dry.
Is ferric sulphate safe for fish ponds?
Yes, in precise doses it precipitates algae-feeding phosphates. Overdosing drops pH and can harm fish, so test water first.