From The Aquarium Wiki
About Magnesium sulphate
To make a typical stock solution for feeding plants add 70g (4.6 tbsp) of dry MgSO4 to 500ml (16.9 fl. oz.) of RO or distilled water and then add once a week 50ml (3.3 Tbsp.) of this solution per 100 Litres (26.4 US G.) of tank.
This will give you 7ppm (7 mg/l) of Magnesium.
- Also used in a ration of 1:3 with CaSO4 (Calcium sulphate) (1 part MgSO4:3 parts CaSO4) to make your own GH mix for a freshwater aquarium.
- Also used to treat constipated fish or fish suffering from dropsy as it is said to help fish expel excess water within their bodies.
- Typical treatment for fish is prepare a quarantine tank and add 1 tbsp per US gallon 3.8 Litres (1 US G.) and immerse freshwater fish into it for 10–20 minutes up to a maximum of twice a day. Repeat this for a couple of days or until you notice the fish passing waste. For aquatic frogs leave in the water for an hour per day.