Jumping pH and rapidly dropping EC

Hi there,
So I have:
-600W Dual Spectrum HPS,
-Wilma 4 pot system,
-Medium is clay pebbles ( in these I grow 2x Vanila Kush, and 2x Critical Kush, both from BF),
Nutes:
Plagron Hydro A+B,
Hesi Super Vit,
Hesi Root Complex (used for first 4 weeks of veg)
Big Bud and Ovedrive (haven't use them yet,as plants are in first week of FLO)


Problem:
On veg pH was going up every 12h from lets say 5.5 to 6.3 and needed to be adjusted with pH down every time, twice a day. For first 3 weeks I didn't use any nutes but pH was unstable anyway, after adding Hydro A+B, Root Complex and Super Vit, nothing has changed. Didn't make any difference was that new nutrient solution or a week old. Solution prepared from tap water (pH 6.9, PPM 220 micro Siemens). On Veg there was no deficiency visible and PPM was going down on rate 60-80 every 24h. Plants were fine for PPM between 1100 and 680. They were not reacting well for pH over 6.3 (i have 2 pH meters, both HM Digital PH-80, both calibrated weekly so pH reading must be right)

Since switching to 12/12 nearly 2 weeks ago (all plants now in FLO), my girls reacted very bad for Hydro A+B in rate of 80% what producer recommends (1000 PPM) showing some nute burn on new leaves and nitrogen toxicity. They were flushed with pH water and seem to be fine, nute burn was not spreading to other leaves (PPM brought down to 680). That was 9 days ago. However, from that time any nutrient solution with PPM over 700 is dropping to 450-430 within 24hrs and girls showing yellow tips again. Then it is going down again on ratio 80-100 PPM for every next 24h till it reaches 300-350 PPM.
What is interesting, pH was always going up with higher PPM values, but since it came down to around 400 PPM, pH actually is rising rapidly every 24h. Sometimes it's going from 5.5 to 6.3 in 9 hours (happened on fresh nutrient solution). When PPM hits 330-350, pH is stable for whatever period of time PPM stays on this level.

Question:
What's the reason for pH going to extremes every 12h? Wrong nutes for my type of water, shitty nutes or what? That's my first hydro but as far as I know, my friends using the same nutes adjust their pH once, maybe twice a week, not every 12 feckin hours :/
Is it normal for EC to be dropping so rapidly and for plants to react so bad for mid-high EC levels?
Any tips, ideas, advices Mates?
2 of 4 plants ( both Critical Kush ) look well but both Vanila Kush are disappointing, one is 40 cm high, growing slow, and other one looks like feckin lettuce from day one.
I don't wanna fuck up that crop so please help me if u have any ideas what's going on.
I want to make sure that they are getting enough nutes to keep them going nice and healthy but I don't want to burn them at any stage from now on.

Appreciate your help Mates.

Did you perhaps switch to flower feeding schedule right after switching to 12/12? If so it's possible your plants are starved for nitrogen. During that initial flowering stretch, their metabolism goes into overdrive and actually needs shitload of nitrogen.

I'd try is changing nutes VERY often, for example every day or two days for a week. So, EC goes from 700 to 300, you give it fresh res at 700. If the plants are missing something so they drink it all in a day or two, that might give thim an oportunity to restore their reserves.

As for pH, its normal that it fluctuates with drastic EC changes.

How are your roots btw?

Thank for your answer Spanky,
Roots are fine, that was the first thing i checked.
Story with plagron hydro A+B is that you keep the same proportions of A+B for bot, veg and flo, so I didn't change anything, keeping them 1:1.
After switching to 12/12 and keeping same feeding schedule they got nute burn so i put down half of nutes not to burn them again.
After that nute burn some leaves showed signs of nitroge toxicity so I don't think they starving for nitro.
No sign of nitrogen deficiency as well.
Just maybe they are short of calcium due to quite low pH as there are some brown spots on leaves.
What I am doing right now is I am adding 8l of ph water with A+B every 2 day once the EC has dropped to around 320-350PPM. That allows to rise EC to 430-450 again but girls are eating that within 24-36h.
Sometimes after that they show little nute burn again. I'm bit confused what to do, but I might top up nutes to 700 PPM as U said and see how it goes.
Am I right thinking that if EC is not dropping so drasticly girls have enough of food and not starving?
What is the normal EC drop for Flo within 24hrs from your experience?
Mine was around -50 to -80PPM per 24h but pH was still going crazy. Bit worried about that as it is pain in the ass to keep pH within range, adding pH Up or Down every 12 h or so.
Thanks for your reply

FIrst of all, it is not recomended that you top up with nute solution. Reason is that your plants might be drinking lots of something and very little of something else. When you top off with nutes, you add some of the stugff they ate and some of the stuff they didnt. Result is a bucket with some of the stuff they are eating and sh*tload of stuff they are not. Your EC shows normal values as overall quantity of dislolved salts is not high, but plants show signs of toxicity as the ratio of disolved salts is off.

As for the pH, it can change very rapidly when EC is low and there is not much stuff to buffer it. I have seen it go up from 5,8 to 6,5 in a day and be down to 5 with just one drop of pH down (I have to disolve the concentrated acid 100 times in order to be able to fine tune my pH).

This is my first hydro grow so I can't tll you whats normal for flower, but mine are drinking 80 EC a day easily, so 100 in your case does not sound impossible. How big is your res (per plant)?

I have plants in wilma system, usually I fill res with 32-35l of solution.
What you wrote down aout topping up nutes makes perfect sense as I get nute burn even with low EC.
I was topping up solution always with 8l of water mixed with nutes about 70-80% what producer recommends.
From now on I'll be mixing new solution every time needed.
So when do you mix new solution, every 7 days or more often as needed, ie when EC goes too low?
Thanks for that precious info m8

acidart said:

From now on I'll be mixing new solution every time needed.
So when do you mix new solution, every 7 days or more often as needed, ie when EC goes too low?

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Weekly reservoir changes are pretty common - I wait sometimes up to 2'ish weeks if plants are small/hardly feeding. When the plants get bigger, you might even need to do changes more often than weekly. But yeah, by monitoring EC you can sort of tailor your own reservoir change schedule as needed for your specific plants and how you grow.

Thanks SableZen, appreciate that m8

I have found that by day 5-6 in peak flower ph will start to drop rapidly and that is when I do a complete refill. Im also a newb and dont top up just to keep it simple.

Info I'm missing is what EC is too low and requires res change.

Spanky84 said:

Info I'm missing is what EC is too low and requires res change.

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To be honest, I wouldn't know what to tell you specifically other than I increase the nutrient strength if they are feeding a lot more than they are drinking. Or vice versa, if they are drinking more than they are feeding, I'll lower the amount used w/ the next res change. Ideally, I like to see the EC (and consequently, the pH) remaining the same as the res level goes down.

My ec actually goes up a bit at at time by around .15 every one too two days. Its the PH i watch re res changes. I have a bitch of a time trying to find ec levels that drop slightly so gave up lol.

Sorry i typically run 1.2-1.4 ec. At beginning of res change.