Beginner Gardening: Marigolds - Low PH?, 1 by PerfecTommy07

PerfecTommy07 wrote:
Hi,

I have some Marigolds planted in containers with some peppers (Key Largo). Some of the foliage on the marigolds are beginning to develop spots. The pepper leaves are also not as dark as they should be. They are a little on the lime green side. I believe this was one of the last containers I potted up and I was running low on the compost and other ferts. Otherwise this is just a standard miracle grow potting mix.

I have done a little research on line and settled on a theory that this (Marigold symptom) is due to an Iron toxicity issue caused by low pH in the substrate. From what I understand it can be remedied by adding some garden lime to the mix.
I could be completely off base, which is why I am here seeking advice.

Does anyone have an alternative diagnosis and/or treatment method?

Also, IF lime is the answer; what is the correct method of application? Can I just mix in a half cup to the top of the substrate and water in? This is a long approx 10 gallon container with 4 pepper plants in with some marigold and zinnias (which seem fine).