Plants Looking Poorly

[Fish are friends]

Hi folks.
Unfortunately i dont have a closeup pic but my amazon swords are looking really poor...the leaves look like the veins are turning brown and there are holes in them.. the new leaves are very pale and generally dont look too good...the other plants in the tank look like they are covered in a black algae and are slightly slimy to the touch...could this be a dosing issue or something else...
the specs are: nitrite 0; ammonia 0; ph 8; nitrate 40 that is what the tap water is...i have sand substrate with T8 lighting...water temp is 26 degrees c...

That is the best pic i have at the moment...

 

[SO19Firearms]

What plant food and CO2 source are you using?

 

[Fish are friends]

right now no plant food or co2. when i set the tank up and planted it the advice was that i wouldn't need co2... what plant food would you recommend and what co2 method would be fine!

 

[ATK!!!]

You don't need Co2 to keep Amazon swords (but obviously having it makes everything grow much easier). It'll probably be that you need to give them more nutrients. Could you please tell us the wattage of the bulbs and how many you have. The more light you have, the more nutrients and Co2 the plants will need.

 

[Fish are friends]

its a single 18w T8 bulb... I dont have an issue with them growing. the swords have really flourished from a few leaves to what you see...its just the fact they look like they are really weak and have brown veins..