We recommend around a half cup for every 40 gallons of aquarium water. A 10 gallon aquarium will need a 1/8 to a 1/4 cup.
To kill free-floating algae( green water, in freshwater aquarium we typically use a AlgaeFix by API or the ultimate solution is a Ultraviolet sterilizer. Here is a link to an article on our website which gives additional ways to kill or control green water: https://www.aquaticexperts.com/pages/how-to-fix-cloudy-water-in-a-freshwater-fish-tank Here is a link to our chart - How to Diagnose and Treat a Cloudy Freshwater Aquarium Water: https://www.aquaticexperts.com/pages/cloudy-water-diagnosis
Do I have to do a water change if I didn't rinse the filter pad?