Phosphorus excess?

[TonyGr]

-Problem: As shown in photos, I noticed some small brown spots. One leaf has a couple of brown areas at the perimeter. New leaves at top look a bit pale and maaaaaybe a little bit like thin blades
-Medium/grow method: Soil. 20% Biobizz Light Mix (top), 80% Biobizz All Mix (bottom).
Airpot 11 liters
-Strain and age: Blue Cheese Automatic (Royal Seeds Queen), 5 weeks and 2 days old
-Feed and supplements used: Root!t First Feed, Bio-Grow, Bio-Heaven, Bio-Bloom, Top Max
-Water source: Rain water
-Climate and Light Schedule: Lights 20/4. Humidity about 50%. Temps 16-18 Celsius when lights off and 20-23 Celsius when lights on
- Light used: 1xLED 18W 1850lm 4000K and 8xLED 12W 980lm 3000K. Distance to tops 15cm
- Additional info: My ph meter is a cheap one and I don't trust it. So, there is a chance I was watering with low ph, about 5.7-5.8

Photos:

According to a chart I found, symptoms match Phosphorus excess. Any ideas? Should I worry? Thanks in advance!

 

[AutoLowRyder]

Temps 16-18 Celsius when lights off and

16c for a root matrix temp is very low........... 20c is minimum, as below 19c the nutrient uptake is slowed,

low temp = acidic soil........... = below Ph 5.6 the phosphorus is the 1st to lock out............ as with yout leaves

ph, about 5.7-5.8

Ph (Potenz Of Hydrogen) is a function of temperature............... get your root temp up, and the nutrient uptake and Ph will rise back to normal.

To check the soil condition, re Ph, get 100mls of fresh run off, using zero nute Ph 6 water, 2c above your root temp, when at 20c................ take the Ph of the run off, if below 5.8, your soil is to acidic....... and is affecting mobile nutrient uptake,.......... hence you PO4 phos deff, creeping in.......................over feeding an Ec that is above 1.2 (Nute Only) will also acidfy the root matrix.............

How to reverse low soil Ph, = raise the temp to 20-22c......... = raise light out temp with 1kw thermo fan, this wil raise root temp. Once raised, lift your normal feed Ph to 7.5, using bi-carbonate of soda or silicone, and keep this going in, untill your run off test (Every other watering) shows the Ph returning, rising in the soil to 6.3 or above, not greater than 7........ your deff will disappear....... you are aerly on in the grow 5wks...... if a fem i switch to 12/12 at 35 days 5 wks as i like a big frame for flowrrs......

it cant be a phos excess as you are still in veg,........ phos is dominant in flower nute regimes not veg....... excess nutes as above cause low Ph in soils, after weeks of feeding high Ec's, over a 100 days of feeding you may flow through one 15ltr pot 300ltrs of feed, that is a lot of salt transit, if the plant aint using it, it will build up in the soil acidifying it to a low Ph....... as chart above.... ALR

 

[Waira]

no way it's P toxicity, not with Biobizz's mild organics,...
Lights are only 15cm away, is that right? Waaaaay too close, back them up to at least 18",.. I need more leaf pics too, whole plant, in normal light please, I can't see enough to diagnose....
...in-pot pH could be off, but let's see other things first... I agree with ALR too on the cool temps, this impairs uptake and metabolism in general,... it needs to warm up more at lights-off period especially,...

 

[AutoLowRyder]

whole plant, in normal light please,

fair comment................. the leaves shown are at the bottom of the plant, not near the top where heat stress or light burn would hit first, maybe ??............. over the years reading, re nutes, biobiz refers the marmite affect. Some hate it others learn it's foyables...........

 

[TonyGr]

I uploaded more photos, with natural light.

 

[Waira]

warm things up, and let's see how she responds,.... adding more nutes may make matters worse if they aren't being taken up well due to cold T's,...

 

[TonyGr]

warm things up, and let's see how she responds,.... adding more nutes may make matters worse if they aren't being taken up well due to cold T's,...

Thanks for feedback. Much appreciated. Harsh winter this year. Made some changes and raised temps around 19-20 Celsius. Still working on it for better performance