[CobraGuppy]

Do you have c02?

43.7 gallons is plenty big enough to start using ferts. Here's a thread i used when i began using dry ferts on my 29 gallon:

http://www.plantedtank.net/forums/water-parameters/21944-_dosing-regimes_.html

You might get more help in the Water Parameters section of the forum though, maybe a mod can move this?