Cal/mag deficiency?

Hi all, currently growing an photo( mass medical) and put an auto in aswell as I usually do. I noticed that the auto is developing brown rust spots( it's not fungus as nothing comes off when rubbed). Both plants are in plant magic soil being fed Bacs nute line. The auto is on half strength compared to photo. I feed nutes every other water and pH is 6.3-6.4. temps are around 26-27°c rh is around 50% . I don't suppliment calmag as my water is pretty hard. Does anyone have any ideas?

Also I forgot to mention it's only affecting the upper leaves

Most common: Calcium / Magnesium or/and PH
Did you slack off on checking PH after mixing up nutes?
Is your PH tester reliable and accurate?
What is the PPM of your water before adding anything?
What is the PPM after adding nutes?

"Also I forgot to mention it's only affecting the upper leaves" Are you using a new water supply or have you always being using the same water?

If your water is around 200 - 300 ppm before adding then there probably isn't a lack of Calcium.

Calcium deficiencies are often caused by low pH at the roots, so that being said... are you watering until there is enough runoff?

Rusty brown spots can also be a sign of a magnesium or calcium deficiency, though they more commonly result from a lack of magnesium than calcium.

My solution would be to add 200ppm of CalMag, then 400 ppm correct nutes, triple check PH of 6.5 and hit it with a nice heavy drench until runoff. Get the soil back on track.

Little-Leopard said:

Most common: Calcium or/and PH
Did you slack off on checking PH after mixing up nutes?
Is your PH tester reliable and accurate?
What is the PPM of your water before adding anything?

"Also I forgot to mention it's only affecting the upper leaves" Are you using a new water supply or have you always being using the same water?

If your water is around 200 - 300 ppm before adding then there probably isn't a lack of Calcium.

Calcium deficiencies are often caused by low pH at the roots, so that being said... are you watering until there is enough runoff?

Click to expand...

Water is 275/300 ppm before nutes. Water is left with bubbler over night. I water untill I get around 10% run off. As for pH meter it's a blue lab, I've checked it in ph7 solution and is calibrated correctly. I have since given her a full flush with 6.2ph water (30l through a 7l pot) and last part of flush was a feed with half strength nutes. The plant itself looks healthy apart from this