Yellowing and spotting on fan leaves

Hi,

Looking for second opinions on what could be going on with one of my plants.

She's GHS White Widow, DWC, 400w HPS, she is 16" tall and in her 2nd week of flower. A few of the bottom fan leaves have yellow patches and some brown spotting. Some of the fan leaves in the middle are also starting to show the same signs, just not nearly as far along. Rest of the plant looks fine.

With the research I've done it looks like its a lack of Phosphorous?



Cheers,
SB

Ca/Mg and possible pH problem.

listen to dr who, he knows his shit

Thanks for your input. On Saturday I upped the cal/mag so hopefully that was the right thing to do and aligns with your suggestion. Just need to wait and see now.

As for pH, I calibrated my meter last week and keeping the reservoir between 5.9 and 6.1.

Cheers,
SB

ph is hydro is best at 5.5-5.8 they seem to be able to intake all the spectrum of nutrients givin. if its higher or lower then the intake stops certain nutrients from being ingested witch in-turn will make leaves yellow and spot or burn.. if it were me i would do a complete flush and refill res. with new water and nutes with the proper ph.. I also add a few tsp of hydrogen peroxide to the mix.. good luck and KEEP ON GROWIN..

So the plant seems to be doing better today after a couple of adjustments on Wednesday.

1) Added GH Subculture-B
2) Upped the pH to 6.2
3) Reservoir temp from 16.8C to 19C. (Automatically happened after adding in the Subculture-B)

Personally I think it was #2 and #3 together that helped, So this weeks water changed I made the water exactly 19C and set the pH to 6.2 and left the subculture-B out.

I'm also finding that my pH meter gives me different readings depending on the water temperature. Guess I'll just wait and see this week on what happens.

Cheers,
SB