HELP!! Possible Mg Def ?

[hoods1975]

Hi all,
I am at the end of my 4th week from switch and some fan leaves at the top and middle are starting to yellow.
I think it's Mg def and would be real grateful for a professional to diagnose this.
Another issue could be my water being 0.8 EC and PH 7.1 out of the tap.

The strain is Great White Shark (GH) in loose rockwool (hand watered).
My nutes are Canna Aqua and i half the dosage they say on the bottle and that brings me to EC 1.8 (inc 0.8) PH'd to 5.7.
So i'm not sure if the feed is too strong.
Temps are a steady 78-80 (600 HPS) and RH 40%.The water is at 21 degs before i hand water them and i have been leaving the pots to dry out a bit (5 days) befor the next feed.
Thanks for your time
Here are some pics

 

[Ziggaro]

Hey how are you? That does certainly look like a mg def with the dark green veins and interveinal chlorosis. But starting with tap at .8 EC is definitely dangerous. That is equal to about 500-600 ppms to start!! Ed Rosenthal MJ Horticulture bible states "If raw water contains more than 300 ppm (~.4 EC) of dissolved solids, use a reverse-osmosis device to purify it"
Could definitely be mag deficiency, but I wouldnt say just adding mg will solve it. Do you know if your water has a high calcium level? Calcium and Magnesium will compete and lock out one another so be careful!!
Have you been using the tap water for the entire grow??

BTW, Im not an expert. I do have plants but I may be even less experienced than you, so if you want expert help, youll probably need to fill out the questionairre in Stitchs sick plants sticky. happy growing!!

 

[hoods1975]

Thanks for the quick reply Ziggaro.
Yes i have been using tap water throughout and had a few symptoms in veg as well.
Not sure about the properties of my tap water but i think a change to bottled water is needed.
Thanks again

 

[Ziggaro]

Cool, id check back though and see if stitch has any advice for you. You may end up needing to flush if this condition progresses.

BTW- bottled water should be either distilled, or reverse-osmosis. DONT BUY DRINKING WATER as they add extra minerals for taste, and a lot of times its sodium which can be bad for your plants. Just remember that you'll probably need a source of cal and mag for bottled RO or distilled water. Peace

 

[Hazeseeker]

yeah looks like Mg from here Hoods. Hazeseeker

 

[hoods1975]

Top advice guys thanks a million.
My local supermarket has bottled water with 0 ec and ph 6.2.
Would this be ok or shall i go for the RO ?

What system are you running? = Passive (hand watering)
What STRAIN are you growing? =Great White Shark
What was the establishing technique? = Seed
What is the age of your plants? = 8.5 weeks
How tall are the plants? = 1.5 – 2ft
What PHASE are the plants in? = Flower
What Technique are you using? = Potponics
What substrate/medium are you using? = Loose rockwool
What is the Water temperature? = 21 degrees
What color are your roots? = White
What Nutrient's are you using? = Canna Aqua (half strength of what bottle says)
What is the TDS/EC/PPM you are using? = 1.8 ec (0.8 ec to start)
What is the pH of the "Tank"? = 5.7
Are you sure your calibration is correct on your equiptment? = Yes
When was your last watering? = 9/1/08
What is your water temps? = 21 degrees
When was your last feeding change? = 4/1/08
How often do you clean your system = Flush every 3 feeds
What size bulb are you using? =600 HPS
What is the distance to the canopy? = 20”
What is your RH Factor(Relative Humidity)? = 40-45%
What is the canopy temperature? 78-80 degrees
What is the Day/Night Temp? = 78-80 (day) 65-67 (night)
What is the current Air Flow? (cfm etc.)
Is the fan blowing directly at plants? = Yes
Is your water HARD or SOFT? = Hard
What water are you using? = Tap
Has plant been recently pruned, cloned off of or pinched = No
Have any pest chemicals been used? = No
Are plant's infected with pest's = No

 

[Ziggaro]

yeah that water is fine the less the EC the better so u know exactly what your plant gets.
Do you have ventilation, or just a fan blowing at the plants?

 

[hoods1975]

Yeah i have 100 rvk for intake and 125 rvk for exhaust both controlled by a prima klima.
I will get that water then , got to be better !
Peace