It sounds like you just don't have enough light to adequately grow plants. Amazon swords are supposed to be able to grow in low light but they don't really thrive. Any growth you have will be negated by the leaves that die on you. Also, I think it takes a while for the roots of an Amazon sword to take hold but when they do, the root system is elaborate and growth should be better. I'd say this will take about two to three months.
The light bulb should actually say how many watts it is on it, although if it's just a single florescent tube it's probably around 30 watts. Then you need to divide the number of watts by the gallons of water in the tank. So if you have a 30 watt bulb in a 30 gallon tank you have 1 watt per gallon. Ideally, even for low light plants, you should be up a little higher, say 1.5. When you get to 2-3 watts per gallon then you have moderate lighting and above 3 watts per gallon you have high lighting.
Since you're on a budget, I would see if I could find a florescent strip light at a Home Depot or local hardward store. This will be much cheaper than buying lights specifically for the aquarium. The downside is trying to get them to fit but I would look around. I know I've spent far too much money on "aquarium" lighting myself.
Before you start adding any fertilizer your first priority is to get your tank cycled. If you're not sure what that is you need to read up a little more. Your second priority is to get more lighting. If you don't have enough light then your plants won't grow and fertilizers will just screw up your tank, probably by causing unwanted algae to grow. There is also a type of clay that is high in iron called Laterite that can be added to your substrate. Generally, it goes on the bottom layer but if you've already put in your gravel then it probably doesn't make sense to add it.
Once your tank is cycled and you have more light then you can think about fertilizer. There are generally two types for the aquarium, liquid and root tabs. Make sure they are aquarium fertilizers because otherwise you will be adding nitrates and other "macronutrients" to your tank, which will cause problems. You want fertilizers that contain "micronutrients", mostly iron and other trace minerals. Use liquid fertilizer for plants that get their nutrients from the water column and root tabs for rooted plants, like sword plants.
You might want to try some other plants that might do better under low light conditions. One plant that I've had very good luck with, and I'm even considering just growing that just so I don't have to worry about plants anymore, is anacharis. It grows quickly under low light although it is much fuller and greener under brighter light. It will help keep algae under control as it will outcompete the algae for the nutrients in the water.
Good luck. Let me know if you need any more advice.
The amazons leaves are nearly all brown now, what should I do. The lights are on 10hrs and the tank also gets some natural light. They are planted in smallish gravel, I havent added any fertiliser or anything. Could it be the temp? I have to check the temp, as I am not sure if my heater is working properly.
