I noticed the stems of some plants, namely the black-eyed peas, starting the lean on the sides from the weight. It could be from too much water, or the fast growth. I had to provide support to the stem to help the plant grow properly.
So, I used barbecue sticks to support the stem.
You insert the stick in parallel to the plant's stem into the hydroton, then tie the stem with a small thread to the stick. I'll keep monitoring the growth & see how positive was this solution.