Auburn spots and droopy leaf-tips

[Atako]

Hello!

Please tell me what's wrong with my plant.

First Problem:
Some of the biggest, oldest leaves start getting auburn spots and dry tips.

Second Problem:
Some leaves have droopy tips.

But overall it has a nice green. No yellow spots sighted, not even a bit.
My suspicion is a potassium deficiency. Am I right? Shall I just fertilize more?

State: 45 cm (~18 inch) height after 25 days of growth. Now flowering since two days.
Strain: Sensi Star (Hungry?)
Lamp: 400W MH, then 400W HPS
Soil: Special-mixed from my local shop, "well pre-fertilized", enough perlite, airy consistence, seems to be a very good soil.
Pot: ~25 L (~6.6 us gallons)
Water: I have a high PH here (Over 8) so I am using PH-. I am always correcting down to ~6.8 - 6.6.
Nutrients: All of BioBizz. Below there is my schedule.

Thanks a lot!

Water in liters, nutrients in milliliters, G/B is Grow/Bloomweek, (height in centimeters, stem in millimeters):

 

[hazy]

I think you need to back off the nutes a little.

 

[Atako]

Thanks for your answer.
I really can't believe that I gave too much.
I gave FishMix in 1:1000 one time about a week ago, and BioGrow 1:1000 the first time about 5 days ago.
The plant shouldnt have absorbed anything of the BioGrow yet.

 

[COhomegrown]

Nice to see another person on here using BioBizz!

I have used Bio for about 3 years now and recently started noticing the same spots you have. Personally i think they are Calcium deficiency spots but im not entirely sure. as far as the droopy tips i only saw one example in your pic's that didn't look too bad. I have had that problem with some of the seeds(Kush-Sage, SSH) that i just planted but its a more severe curl down which i am thinking is N over fert.

Well ill pull up a chair for this one always good to find info from other bio-bizz users.

 

[hazy]

I have no experience with bio bizz nutes, but I'm sure they are great.

You do have a calcium def.
You can see the small brown spots. a few. Calcium and mag deficiencies are always caused by low pH in the medium.
Low pH causes dissolution of iron making it too available and it precipitates with P and ties it up.
iron, mang, zinc, boron, copper, all become more available when pH goes down. molybdenum decreases.
Calcium leaches, which was buffering the pH up. in soil, aluminum will be made available and is toxic.

Fact is, it only matters what the pH is in the root zone. all deficiency/toxicity problems are pH related. Your soil is 'pre-ferted', so do you need to add any nutes at all?

It really doesn't take much nute concentration to lower pH of the medium.

 

[Atako]

First, thanks for your answers.

I have a very accurate PH-meter; this one (Greisinger):

Relatively new and just recalibrated a few weeks ago. I am always measuring and correcting the PH after mixing the additives with stale water. I didn't water with under 6.6 so I wonder why the PH is wrong.
I thought 6.5 would just be fine.

Could it be that the soil PH was already low from the very first and increased just very slowly because I always watered with ~6.8 - 6.6?

However, I have flushed the soil well yesterday (my tap-water is around 8+) and gave 1000:1 BioBloom and FishMix, final mixture PH 7.0.
I hope that the plant can recover, but now the topmost leaves are not so lush-green than they should be.

I don't think that I don't have to add nutrients at all.
The shop staff told me that the pre-fertilization should last for 3 - 4 weeks. The soil contains special "coated" (very little) pellets, emitting the nutrients slowly and consecutively.
1000:1 of BioGrow is really not so much.

Here you can find the official BioBizz growth schedule:
http://www.biobizz.nl/downloads

I think my soil can be compared best with BioBizz "All-Mix".

Anyway, for the next time I will always water neutral with PH 7.0, or what do you advise me?

I remember, long time ago, where I had the same Problem with these spots on the leaves. There I never corrected the PH and always watered with fresh tap water with PH around 8 or more.
Then, in another forum, they advised me to correct the PH because the soil can't do it's buffering function with so high PH values well.

Hmmm....