White leaves.

I have 5 plants that are 17 days into flowering. They have very pale/white lower leaves but they still seem firm and have no signs of burn. The stems have reddish stripes on them. I have been feeding with BioBloom at 4ml/L every time they get dryish. I am using coco for my medium in 3 gal buckets. I'm using a 400w HPS. My temps hover around 78-80 degrees.

I heard this could be a Mg deficiency. Might it be caused by overfeeding? According to the website, BioBloom is a complete plant food with micro-nutrients and so on. Should I try a foliar spray of epsom salts? If so, what concentration?

Today I flushed them and added 1/2 strength ferts afterwards. My ph was a little low at about 6.2 before flush.

Sorry I don't have pics. The plants look healthy except for these white leaves and red stems.

Thanks for your time. :)

As a matter of fact, your pH is not low at all- you are in coco, so you SHOULD be lower than the soil range, since coco is technically a soilless/hydroponic medium.
How many of the lower leaves are pale? And are they leaves that don't get much light? It could be Nitrogen deficiency or simply unused old leaves dying off because thye no longer serve a purpose to the plant.
It doesn't sound like Mg def.
Don't let coco ever dry out completely BTW.
One way to determine feeding strength is to up your fertilizer just a little- keep track of what you're using and creep up to the point where you see a tiny bit of scorch, then flush and from then on feed with the highest level that DIDN'T burn your plants.

Thanks very much Stinky. That makes sense with the coco. There is one plant that has about half of its leaves that are yellow, it is also the biggest one. I recently repotted so maybe it was rootbound? The rest look fine. I was just worried because I thought it was too soon to be yellowing before harvest. None of the leaves have fallen off. I'll just keep an eye on them. Thanks again.

Even so, I'd give them a bit more food and see how they react. You are only in week 3 so you have quite a ways to go. Half yellow should not happen until a week or 2 before harvest at the very earliest.