Results of nitrate/phosphate results?
Are you using RO/DI water to make your salt water?
How often and how much of water changes are you doing?
Typically diatoms are from excessive silicates in the system.. Provided you aren't adding them back into the system they will clear on their own as the silicates are consumed by the diatoms..
Algae is from elevated nitrates and or phosphate levels.. Thats usually from too little maintenance (lack of sufficient water changes.. dirty canister filters.. ,etc..) and also from over feeding and over stocking of the tank (too much food or too many critters)
4 months old is still "new" and it could all simply go away on its own as the tank gets more mature..
In addition to the questions above it might help to describe the tank..equipment you are using,etc...
oh and GFO is granular ferric oxide (basically rust) is a chemical use to remove/bind phosphate in water..
