Water-related deficiency?`

See attached photo. These plants were grown with untreated tap water as an experiment. The purpose is to find the right water treatment. Previously, I've had several successful grows using rain water and distilled water. Drought has reduced rainfall, so that's no longer dependable.

Miscellaneous info:

• Plants: six (cultivars: white widow and purple kush)
• Age: approximately 3.5 months old (5 weeks in veg stage)
• Soil: 80 percent FF Ocean Forest, 20 percent perlite
• Nutes: 2 tsp Tiger Bloom, 0.5 tsp Superthrive per gallon at every watering
• Lighting: 84,000 lumens (400w HPS overhead and CFL side), 2700K spectrum
• Light cycle: 12/12
• Temperature: ventilated room with temps that range from 78 to 89 degrees (F).

Water:

• pH: 7.8
• PPM: ????

What's happening here? What changes should I make for optimum growth and yield?

Looks more like the inadequate amount of lime (oyster shell flour), that is in FFOF has run out. This could lead to both pH issues and a lack of Ca. Did you add lime to the mix?

It could be the water, but I don't think so and would look elsewhere.

Wet

That's the only variable that's really changed between last grow and this one. I think rainwater has a pH of about 6.5, distilled is 7.0.

Is the tapwater with a pH of 7.8 alkaline enough to lock out some nutes?

Also, this problem became apparent only a couple of weeks into the grow, so it's been fairly consistent. The fan leaves grew just fine, but then became necrotic after yellowing like this.

E... said:

Is the tapwater with a pH of 7.8 alkaline enough to lock out some nutes?

Click to expand...

Well, yes and no.

7.8 is high enough for a bit of lockout, but any liquid is only going to affect the soils pH for a very limited time and the soil will buffer it to whatever pH it is.

My tap water ranges from 7.3-7.5 or so and I dump stuff on there with pH ranges from low 5's to over 10 and the soil brings them all into a 6.8 or so range.

IDK for sure, I haven't had my meter out of the box for 8 or 9 months.

Wet

I got some distilled that was Ph of 4.5 from Albertsons. Shoot for 6 not 7.