plants suffering from somethin

[Tropjunky]

i have a 12G tank with a CO2 system that i made myself and some of the plants start to get yellow it starts from the edges and moves in. is this a nartal process or do i need to feed my plants

 

[George Farmer]

What plants, lighting and substrate do you have? CO2 is only really useful when you employ sufficient lighting and depending on the species of plant, have a nutrient rich substrate?

The yellowing may be lack of light or nutrients or both. Let us know a few more things about your setup and we should be able to help furthur.