What causes plants to have yellow leaves ?

[angel12]

As above what is the cause and how can it be adjusted i am asking this on behalf of a friend of mine also his leaves have tiny spots on them surrounded by yellow is this lack of iron .. he has Activated Carbon in his filter does he need to take this out ...

if i need to supply more information can you tell me what you need to know ...

[ronrca]

Carbon goes out! I do not use carbon in any of my tanks unless I need to remove meds! It is said that carbon filters remove necessary nutrients required by plants. If that is or isnt the case doesnt really matter. Carbon is simply not needed as a regular filter in a tank.

As for plant symptons and remedies, check this link out:
http://www.csd.net/~cgadd/aqua/art_plant_nutrient.htm

Another link about carbon which is very interesting:
http://www.drhelm.com/aquarium/carbon.html

[Paulio]

Check out Chuck Gadds planted tank page. He has an excellent nutrient chart.

http://www.csd.net/~cgadd/aqua/

[ChloroPhil]

It sounds to me like a lack of Potassium and traces. Lack of Iron doesn't usually create holes in plants, but lack of other nutrients, like Potassium and Calcium, will. I recommend Tropica Master Grow or Seachem Flourish to remedy this.