[Edward]

Dosing small aquariums is easy. For example PPS-Pro fertilizing dose is 1 ml per 10 gallon or 40 liters a day. For your 3.7 gallon aquarium the dose would be 7 drops a day solution #1 and #2. To do this you can get an eye dropper from your local drug store or pharmacy.

 

[Edward]

... i dont know where to get dry ferts, ...

http://www.greenleafaquariums.com/
http://www.aquariumfertilizer.com/
http://www.hydroponics.com/
http://www.plantprod.com/

 

[Edward]

PPS-Pro daily dose is 1 ml / 10 gallon or 40 liters aquarium.

examples:
1 ml / 10 gallon or 40 liters
5 ml / 50 gallon or 200 liters
10 ml / 100 gallon or 400 liter