Help me Identify leaf issue.

[Blent]

One or 2 leaves have developed these spots over a fairly long period of time... Plant is otherwise looking very healthy. 6 weeks into flower RDWC pH 5.7 @1200pm 2part bloom nutes 20-10-40. + Calmag + Epsom Salt. Humidity 50-60% Res temp 18c air temp 22c.
I've been noticing a slow and steady drop in pH over time which is easily corrected and ppms remain stable with a water drop of 3l per day.
Any ideas what is causing this?
You can also see a leaf in the bottom of the bud pic that appears to be nutrient deficient. It may be that I've depleted all nitrogen.
TIA

 

[Logan Burke]

If you're applying Cal/Mag then you should be safe to remove the Epsom Salts, since they're primarily adding Magnesium to your nute solution. Adding any nutrient in excess can affect the balance and uptake of other related nutrients such as Calcium. Personally, being in DWC as well, I always get a degree of PH drop in flower, mid flower specifically. I don't think you're deficient in nitrogen, you'd have a bunch of yellow leaves at the bottom of the plant. How much is your PH dropping a day? If it's only 0.1-0.2, I wouldn't stress to bad. When I begin to add too much bloom boosters (high P supplements) I tend to get very similar legions on my larger sized fan leaves. I suspect it's because high P can block the uptake of magnesium, no matter how much you Cal/Mag you add. We will start crossing out possible causes and try to get this fixed

 

[Blent]

If you're applying Cal/Mag then you should be safe to remove the Epsom Salts, since they're primarily adding Magnesium to your nute solution. Adding any nutrient in excess can affect the balance and uptake of other related nutrients such as Calcium. Personally, being in DWC as well, I always get a degree of PH drop in flower, mid flower specifically. I don't think you're deficient in nitrogen, you'd have a bunch of yellow leaves at the bottom of the plant. How much is your PH dropping a day? If it's only 0.1-0.2, I wouldn't stress to bad. When I begin to add too much bloom boosters (high P supplements) I tend to get very similar legions on my larger sized fan leaves. I suspect it's because high P can block the uptake of magnesium, no matter how much you Cal/Mag you add. We will start crossing out possible causes and try to get this fixed

Great reply, thanks. Only dropping .05 to .1 pH per day. I do have a fairly aggressive bloom booster that I had been phasing in gradually so that might be on the money. No significant yellowing to speak of.
I'm not too concerned really as the rest of the plant is in good shape. The leaves affected are older and very few of them show these signs. I guess you can't expect every leaf on a tree to look perfect. Thanks.

 

[3rd Monkey]

Doesn't look like you're short on N at all. 6 weeks in, I'd back N off to at least half (flowering time dependent).

 

[Blitz35]

If you're searching for the reason why your ph tends to drop more in flower, it's normal. In flower, plants are eating the most, and alot of that is in the form of cations (positively charged ions like calcium, magnesium, potassium...) Each time the plant takes up a cation, it must release a positively charged hydrogen ion in order to maintain electrical balance with your medium, and that hydrogen ion is what ph is..the more you have...the lower it goes. In veg, the plants take up alot of nitrogen, an anion (negatively charged ion, if it's nitrate form rather than ammoniacal form), so the plant then releases a hydroxide ion (negatively charged) back into the medium, pushing the ph up. Hence why, once plants start to use less nitrogen and more cations..the ph will tend to drift down in flower..it's all normal! Ph is simply a representation of the amount of hydrogen, or hydroxide, in your medium. More hydrogen=lower ph..more hydroxide=higher ph

 

[Blent]

If you're searching for the reason why your ph tends to drop more in flower, it's normal. In flower, plants are eating the most, and alot of that is in the form of cations (positively charged ions like calcium, magnesium, potassium...) Each time the plant takes up a cation, it must release a positively charged hydrogen ion in order to maintain electrical balance with your medium, and that hydrogen ion is what ph is..the more you have...the lower it goes. In veg, the plants take up alot of nitrogen, an anion (negatively charged ion), so the plant then releases a hydroxide ion (negatively charged) back into the medium, pushing the ph up. Hence why, once plants start to use less nitrogen and more cations..the ph will tend to drift down in flower..it's all normal! Ph is simply a representation of the amount of hydrogen, or hydroxide, in your medium. More hydrogen=lower ph..more hydroxide=higher ph

Holy shit, that's a god level reply... Well done. Although I wasn't really concerned with the pH that is really good to know.

 

[Logan Burke]

Great reply, thanks. Only dropping .05 to .1 pH per day. I do have a fairly aggressive bloom booster that I had been phasing in gradually so that might be on the money. No significant yellowing to speak of.
I'm not too concerned really as the rest of the plant is in good shape. The leaves affected are older and very few of them show these signs. I guess you can't expect every leaf on a tree to look perfect. Thanks.

Oh yeah I wouldn't worry about that much drop at all! I do know it's hard not to stress when leaves discolor that way because I do the same thing lol. Honestly, unless you're getting new leaves appearing like that everyday, I wouldn't change anything. If that is the case, then yeah I'd try backing off of your high phosphorous supplements, add them still just cut their dosage maybe 25-35% and see if there is a change. If not, then no harm done and you know that isn't the problem. Blitz knows his stuff well, I'm glad he's in this thread!