I have a 180 litre tank and i am dosing 5.5ml a day as my tank is pretty heavily planted. That should last me approximately 6 months as it is roughly double the dose needed.
You can also create you own fertilizer buy buying the powders and mixing them yourself. TPN is all you will need if you do not run CO2, TPN+if you do, which has already been mentioned.
Google James TPN and it will give you all you need to create your own fert. I paid £20 for the powders, and that will last me alot longet than bottles of TPN you buy in the shops. Just a suggestion. I can provide you a link if you want mate.
GEt some plants in there mate Vallis Vallis Vallis