it looks like a phosphorus deficiency and you might have a nitrogen deficiency too.
What are you feeding them?
I always expect the soil to dry while I water it. Maybe it's time for a transplant. I haven't started feeding yet. He's using food in the soil. I'm transferring them this week. We'll see what happens. I'm going to do an update
yes, there's no watering until you feel the lightness thereWhat I recommend to new growers of anything, is take an empty pot, fill it with dry medium, and put it in with your plants. When you go to water/feed, lift a plant in one hand, the dry pot in the other, and if they are relatively equivalent in weight, it's time to water.