Phosphorous deficiency?

[M4A]

I've got some plants going in FD's soil mix that are entering week 6 and I'm starting to get these spots on the lower leaves. I've checked soil ph and its 6.7 on the Accurate probe, ferts are going in at 6.35ish. I'm using the Grow More seagrow 16-16-16 at 3/4tsp per gallon and a little Hawaiian Bud at 1/8tsp per gallon. i'm also adding 1tsp blackstrap per gallon.

It looks like illustrations ive seen of phosphorous def. but I'm not familiar enough to really know. Any ideas? Up until now, these plants have been the biggest growing and healthiest looking I've ever grown, I'd like to keep them that way.

 

[namvet25]

How long have you been using the sea grow? It does look like phos def.Have you been using any cal/mag?

 

[Wait what?]

Molasses has potassium, not phosphorous. I don't know if that's what you were thinking, but I learned it the hard way

 

[M4A]

I've been using the Seagrow for 2-3 weeks and am getting fantastic growth, then this showed. In prior grows I used just ph'd water and would get some issues but rarely this early in a grow. I was using the blackstrap for my Mag, and I've got plenty of cal in the soil mix.

 

[sniper]

You need the 4-26-26 Seagrow bloom the 16-16-16 is for veg the Hawaiian bud is for late flower the 4-26-26 is for main bloom phase

 

[M4A]

I have the 4-26-26 but IMO these plants havent quite hit full flower stage yet

 

[Muddy]

You're right around the time that vertical growth usually stops. Once it does, you're into full flower. Since you're using molasses and not a cal/mag supplement, I'd also suggest you add in some epsom salts. 1 tablespoon per gallon of feed.

 

[M4A]

I have their cal-mag but the instructions said if your soil had calcium (mine has powdered oyster shells) it wasn't necessary. I'm growing under LEDs which is why I've been using the blackstrap. Would you recommend ditching the blackstrap and using just the calmag instead?

Muddy, is this a sign of phosphorous deficiency?

 

[Muddy]

Autos in general, and ones grown under LEDs specifically, usually require more cal/mag and if there is a deficiency, it usually shows up around week 5 or 6, right where you are now. You can use either molasses and epsom salts or a cal/mag supplement but I wouldn't recommend using both.

 

[M4A]

l'll try just using the Growmore maxical cal-mag for a while and ditch the blackstrap. It seems like a really small amount of calmag per qt is called for, its roughly 1/4tsp per gallon according to the info provided by growmore cannabis chart, so that like 1/16th tsp per qt. Is such a small amount normal?