Yellowing Plant Leaves

[ViperJr]

I'm no plant expert but yellowing is usually a sign of too little nutrient. That can probably be caused by your superclean water, if that's their only source of water. Some plants' leaves turns lighter when exposed to much light, but that's often a more whiteish color than yellow.
Perhaps watering the plant itself with nontreated water and see if thag helps?

[John]

Actually I think it's more likely a lighting issue. How are you lighting the terrariums Michael?

[MikeM670]

The lighting in the 40 vert is not as bright as I would like it to be. I have two hoods each with those spiral fluorescent bulbs. I'm not at home so can't say what wattage they are. The other tanks are lighted by 2 regular fluorescent 40 watt bulbs. The plants are overtaking the 20 long I have but I'm seeing yellowing of leaves. I think they are the older leaves. I do plan on changing over to T5's in the future.

[MikeM670]

Viper,

I have thought that might be the issue. I still might add a bit of fish emulation to see if that gives them a boost.

[bshmerlie]

I agree its a lighting issue. I reduce my light hours to eight hours a day during the hot summer to help control heat. By the end of September several of the plants will have yellow leaves. I just trim them. That's the price I pay to keep it cool. They will recover.

[UncleChester]

Too much water can cause leaves to turn yellow, often the lower ones go first if this is the problem and they can eventually rot off. Is the substrate constantly wet or soggy? Damp is usually ok, but wet can be bad depending on the plant. Too little fertilizer can look similar, but if your plants are still growing this is likely not the issue.

Typical symptom of too little light is the plant will stretch and and get 'leggy' trying to get closer to it, not yellowing of the leaves in my experience. Some variegated varieties may tend to a plain green under low light, but not head towards yellow.

[MikeM670]

Too much water can cause leaves to turn yellow, often the lower ones go first if this is the problem and they can eventually rot off. Is the substrate constantly wet or soggy? Damp is usually ok, but wet can be bad depending on the plant. Too little fertilizer can look similar, but if your plants are still growing this is likely not the issue.

The ABG Mix is damp but not soaking and I do keep the tanks damper to maintain higher humidity. I've lost a few bromeliads to rot!

Typical symptom of too little light is the plant will stretch and and get 'leggy' trying to get closer to it, not yellowing of the leaves in my experience. Some variegated varieties may tend to a plain green under low light, but not head towards yellow.

I know the 40 vertical suffers from lower light at the bottom but that is not where the leaves on my lance leaf ficus are turning yellow. Just so many variables on this issue.