Can you post some pics? Maybe too little or too much water?

Here are some pics

And another

Number 3

And finally.

I think a trick with planting in pots is that the plants may be either too wet or too dry. Especially when the plants get big, they take up a lot of water and can dry out the pot really quickly. Have you been fertilizing? Maybe its fertilizer burn?

Applied a liquid feed a couple of weeks ago.