Leaves yellowing, Shriveling, and falling off

[MattD]

Hey everybody. I've been growing for about 2 years now, mostly autos. I'm trying my luck at photoperiod right now. I keep having the identical issue with all of my plants no matter the strain. My leaves start to turn yellow, the limp, then fall off starting at the bottom and working their way up. It's always a race to see if I can get my plants to finish before they lose all of their fan leaves (and then sugar leaves, too). It tends to start when pre-flowering is happening and picks up speed through flowering.
I'm using a 750w HPS (capable of 1000w but I have it turned down).
Indoor Grow
Soil - Ocean forest
Nutes - General Hydro - 3 pack. Full strength every other watering. PH water the other times.
Watering habits - I can never water enough to get to run off because my plants will wilt from thirst before the pot is dry, leading to over watering. I use 3 gallon pots for autos, 5 gallon for photoperiod. I usually end up watering every other day, but with less water per day.
Temp in the room is 77-80 lights on, 72 lights off. Currently in 12/12 on the plant I'm writing about.
Current grow - Girl Scout and Birthday Cake. Both strains are showing the same behavior. I've attached a pic of a typical lower leaf.

I'm stumped. I know I'm missing something but everything I've tried doesn't seem to make a difference. Thoughts?
Thanks everyone!
Matt

[SoOrbudgal]

Man i'm thinking overwatered ph root issue. I lift to check heaviness of pot if it's light i water. Are you getting any runoff does it slowly absorb?

[Rwise]

Not stupid but you gave the answer in your post, you let them dry to the point of wilting, this puts the plant into survival mode and she starts using the water from the big leaves. Then you water but she has already tasted the nutes from the leaf (candy to a kid) and she depletes the storage tank (leaf). It then falls off, no problem just change your watering habit. I do this to force them to defoliate them selves.
BTW I water some of mine every day to 3 times a day, I am outside in 20+ gallon pots.

[MattD]

I've never been able to get enough water in there to get run off without the pot taking several days (4-5) to dry out. By the time they feel light, the top 3/4 of the pot is bone dry and the plants look wilted. Rwise, I think you're on to something here. This would explain why it happens to all of my plants, not just certain strains or types. If I can't get them to run off each time, would watering less each time, but maybe water every day be an option? I can deep water them every few weeks to run off to get the soil cleaned up.
BTW: I usually PH my nutes between 6.3 and 6.7. I tested my soil by mixing 50% soil and 50% ph 6.5 water and I got 6.7.
Thanks for answers!
Matt

[Rwise]

Sounds like your soil could use perlite, about 30-50%, unless you use worms then expanded clay beads (perlite kills worms). This will give better drainage and keep more air in the soil. 6.3 is a bit low for PH with soil.

What kind of pot do you use? Plastic pots, one can add many more holes in the bottom and sides to get drainage an air into the soil.

[MattD]

I've been using fabric pots. I definitely think perlite is a must. I have been adding some, but nowhere near that amount. I usually only add a handful to each pot when mixing it up. What are your thoughts on smaller pots? I've seen recommendations for 1 gallon per foot of plant, which means my pots are too big. But I've also seen three foots plants need five gallon pots. My fear of smaller pots is limiting the overall size of the plant if the roots don't have anywhere to go.

[Rwise]

Exactly, more roots equals more buds! 1 gallon per foot does not work at all, my plants are 6-7 footers in 20+ gallon pots and I have to feed them. The soil when harvested (even smaller plants) has been like a marshmallow with fine roots. The way I see it there is no such thing as a pot that is to big! With more soil it is easier to maintain a PH balance, more forgiving to occasional over/under water, etc.

[MattD]

I Like that way of thinking. I can't imagine taking care of plants in 20 gallon pots! Most of my autos get topped so they never get above 2 feet, but the photoperiod plants are closer to 4 feet tall. That's about all I can handle, but it's perfect for me. I rebalance my ph meter, the low end 4.0 was off a bit so maybe that will help as well. I need to get better at checking it's accuracy more often. Thanks for the advice!
Matt

[MattD]

Here’s a pic of the overall plant. I swear I can see the leaves changing daily. Not sure this one is going to make it. I’m only two weeks into flowering and it seems to be accelerating.