dwc grow - very weird problem

Hello everyone im fairly new to this site so please bare with me.

Ive been growing in dwc for around 4 grows now and i have successfully each time around. aroound 5-6 ounce per plant dry weight.
ive come into an unknown problem this time around and i can not understand what is going on.my problem is a drastic ph drop in 12-24 hours. i know its been said countless times but from what ive read theres has been swinging in flower, whilst on the other hand in my position they have been swinging down whilst in veg. i always set my nutes up in this routine which is this.

i have a 100ltr reservoir (water butt) which is filled with tap water (ec0.6) this is bubbled in advance for 48 hours by an air pump rated at 50lpm,loads of bubbled.
i then fill my 20 ltr bucket up with around 14 litres of this water and add my a-b of nutes , canna aqua vega. ill adjust my ph to 5.8 then let that sit for around 30 minutes till it has settled then reajust if needed. i will bubble the bucket for around 2 hours then adjust my ph to 5.8 as the added oxygen will raise this by a fair bit.once im happy after about 2-3 hours and its stable ill drop the plant into the bucket and leave her alone.when i check on her in around 12 hours its gone from 5.8 to 4 or even lower sometimes. the actual ec i was giving them was around 1.40. that being said it was going down to 1.20 in them 12 hours but ph would go right down too. id then strengthen the mix to 1.60 and adjust my ph to suit her needs. 12 hours later its going down still on the e.c and ph is still going down. what is happening here. these roots are as white as can be but yet im still having these major problems, i since spun them on saturday with fresh veg nutes still as im going to give then enough for the 1-2 weeks changeover until i start giving her flower nutes (aqua flores) my worry is if im having major ph drops in this time around whats going to happen when she really starts dropping in flower. ive always had the ph rise in veg and drop in flower, nothing like this before. what am i missing here.

day time temps 24.2c, night time temps 19c, again roots are whiter than ive ever had,

i was aware that pathogen -rootrot can cause ph drops -swings but i cant see nor smell anything. i have covered my bucket lids and netpots with silver foil tape and masked anylight so ive covered that.the ec is going down so there drinking but ph falls very low after 12-24 hours so they cant drink anymore. so why would my ec go down and not up seen as they cant drink the nutes due to ph drop. i assume it would rise again and be more concentrated. The room i have them in is a controlled room without co2. its nice and cool with plenty of moving air. controlled fans-night time temps fine. ph all over the place, never up just down.

are these plants taking more of one thing (n-p-k)lowering my ph. please guys any help would be great, im not too worried about this as they seem ok. there cupping with the light. drinking heavily on water and nutes.im in a that position were im thinking of just dunking them in cannazyme and h202 for a day or 2 and start again but i feel that wont do much as they have more than enough oxygen in there buckets and the roots are white so no root rot.

pulling my hair out on this grow. really grimds me down when i have to spend 3-4 hours after work just to compensate something that will leave me back to square 1 the following day.

by the way i have 2 plants and there big,well over 1.2 square meters each and there only gunna get bigger from the changeover, there each with different nute brands but both doing the same thing.i will if needed post a video of the journal for others to see how the rooms setup just for piece of mind on there part. ive had 4 successful grows under my belt with this type of growing. this has utterly stumped my expectations.

appreciate your insight guys. cheers.

So scimming through your essay I saw that you are having pH drops in flower fluctuating from 12-24 hours after initial adjustment. You are worried about some root rot.

What I have not seen is how the plants are looking? Your pH may be doing funky things because your plants are eating, long release nute, microbes, etc etc. So watch your plants are they showing effect from this?

Next if you are worried about a rot problem why not flush w/ some 29% peroxide diluted it will kill the root rot. flush through roots and happy days!

Also what is your rooms humidity on and off light cycles?

i think your somehow mistaken by my first post,no probs ill explain again, ive initially had this problem during veg phase,i set my ph at 5.8 after i add nutes, ill bubble the bucket without plant and have to bubble again due to oxygen being put in the nuted water, ill then ph adjust to 5.8 again and when i am happy ill put the plant in the bucket, again this ph drop was in veg roughly from 3rd week onwards. these have been vegged for around 5-6 weeks, i turned them saturday to 12-12 and still i havent seen any stability. i found it if ph balance my nutes to 5.8 it will down to 4.2 then next day, last night 11.45pm i decided to ph up to around 6.2 and let it drift down giving me more time to adjust if needed, just checked bucket 1 and the ph is at 6.00 and ec has gone down also, by around 0.08 so thats roughly in the ball park as thats not too fast but plant is yellowing, odd!!
plant 2 was set at 6.18 last night and it was 6.07 this morning, ec has stayed around the same 1.70, again this plant is yellowing. im sure this is due to the changeover from 18-6 to 12-12. i think once flower nutes are in the buckets they should green back up. i understand a ph of 5.5 - 5.8 is the best ball park figure for dwc, i already know this, my nutes say from 5.2-6.2 canna aqua, and PM says 5.5-6,

so no adjustment was needed this morning i was pretty happy with the readings, hopefully it will drop slowly today giving me enough time to have a check again later, they are drinking so thats the main thing but looking yellow on all new growth probably because there wanting more of a different chemical, i.e flower nutes.

humidity is around 50 % constant night and day, this has been fine all my last grows, i always knock down the humitidy to around 30% the last 2 weeks of flower using a dehumidifier,never had a problem.....
there both new strains to me so i guess you live and learn, ive been growing big bang 2 the last 3 grows,