Random dark spots on random leaves in hydro

[marx2k]

So I'm in the middle of flowering using an Ebb&Flow table filled with hydroton and 5 plants. The table itself is about 3'x2.75'x6". The plants get flooded for 15 minutes every 2 hours. The PPM of the water is about 950 right now and the pH remains about 5.4 to 5.7 depending on whether I just fed or not. The nutrients used are FloraNova Bloom + CalMag+ + Hygrozyme + Floralicious. I've also added a mycorrhizae powder into the res.

The plants are doing great except some leaves on the plants show dark spots on the leaves. The dark spots don't seem to be growing on the leaves, they generally stay the same. There is a swiveling fan on one edge of the table and a lot of the dark spots seem to be placed where the wind from the fan hits the leaves (but not always). Some of the leaves end up falling off (only 3 or 4 so far) while they're still fully green but with a few dark spots. This affects mainly the lower portion of the plants and does not seem to be creeping up the plant. What's also strange is that the leaf will either become dried and brittle where the dark spot is or it becomes rubbery at that location.

Is this some sort of fungus or mold? If so, how do we take care of that with plants a little more than halfway through flower?

 

[HeadyPete]

Phosphorus deficiency probably...what dosage of FN bloom are you giving? How much light? Pix?
Look like this?

 

[marx2k]

Phosphorus deficiency probably...what dosage of FN bloom are you giving? How much light? Pix?
Look like this?

yyyyep! That's pretty much what they look like. I don't really go by measured dose in way of tbsp, tsp, etc. I am keeping the reservoir ppm at about 1000 and it is 90% FN Bloom. I'll get pics as soon as lights turn on but that picture pretty much covers it.

I was trying to go a while not changing the res during flowering and have just been topping up as I've heard people have some success with that. So I wonder if I running a fresh new res will solve the issue. My guess is the plant sucked up more P than other nutes in the res and when I top up, it's not enough P.

Edit: The amount of light is a 430W CMH.

 

[HeadyPete]

I would change it out and if it continues, increase you bloom dose. You are running a good amount of light so they can take it.

 

[marx2k]

Heeeere we go... Pretty much the same type of issue as with the originally posted leaf, agreed?

 

[HeadyPete]

Yep I can see it starting. Are those leaves fresh cut? I also see they are droopy. It may be overwatering. Some close up and far shots of the whole plants would help confirm.

 

[marx2k]

Yes they are fresh cut. The leaves of the plant that are not directly in the light do droop. The upper canopy by the light is pretty tight so not much light gets down below the plant canopy. I expect a bit of droop at that point. Some not in the light on the upper part of the plant (damn plants overgrew the cab and went above the shadow-line of the cooltube reflector) have ram's horns going on. The ones directly under the light look excellent.

 

[HeadyPete]

I think you should try backing off your watering sched to 15 mins every four hours and see how they react.....
Another trick is to give all the plants a quarter spin every day or when you are in there...this allows the buds to form fully because evry side is getting light at some point. This is the cheap man's light mover....

 

[marx2k]

I calibrated my pH meter today and re-tested the pH in the res. 5.09. No wonder it wasn't uptaking Phosphorous.

I've added some KoolBloom (0-10-10) to the res as well and adjusted the pH to 5.56. This should help without me having to change out the res.

I will take your advice and go with 15 minute floods every 4 hours. I originally had it 15 minutes per hour then scaled it back to every 2 hours. With the e/f table I have, I'm pretty sure all of the water is not draining away from the bottom so there is some water left in the table after the end of the flood period. That's bad but there's nothing I can do about it at this point in the cycle.

I am unable to rotate the plants as they are sitting in square net pots filled with hydroton which themselves sit in a table full of hydroton. So those plants are pretty much stuck where they are until harvest. I would love to be able to move them around since they completely overgrew the cab. I had no idea the seeds I was given were sativa dominant and this is my first real attempt at hydroponics and I had no idea how explosive the growth would be. Next time, scrog!

 

[HeadyPete]

Sounds good. PM me if there are any issues that come up, or just with an update of their progress....I would change the rez next if they don't improve in a few days.