Newbie needing help please 4week old plant!!

Hi this is the first grow ive ever attempted!! I bought 5 feminised cheese seeds from greenhouse seeds but only decided to germ 1 incase any major problems occured it wouldnt be a total waste. Conditions =

Indoor Tent 80cmx80cm 160cm tall.
400w grolux dual spectrum cooltube about 97 cm from plant top.
No extraction fitted yet but will have one next week atm just using a clip on fan pointing at light, pushing air through top of zip flap! Natural intake through bottom vents.
Temp Day 24-27 deg celcius--Night 16-19
Humidity aprox 25-35%

Im growing using Passive Hydroponics with=
Grodan Rockwool seed, transplant and growing cubes.
Canna Nutrients=
Rhizotonic for seedling 4ml per litre NPK= 0,6-0,2-0,6
Canna Hydro Vega A+B Hard Water. 1ml per litre NPK= 6 - 2 - 8.
I water 1-2 times daily with little run off or when pot feels light
Im using Hard tap water ph around 7.0+ after nutrients ph rounded off to 5.5-5.8

So as you can see in the pictures the leaves are loosing colour with white patches appearing on older leaves, same thing happened with first true set of leaves which no longer exist.
At first i thought it might have been spider mite so sprayed with SMC twice over a week but a week later second set are facing the same fate!

Next week i'll be getting a new 125mm extractor fan, Cannazym, Canna Nitric Acid PH Down and Hesi super vit.
Untill then any recomendations or help will be greatly appretiated

If you need further info on nutrients or anything else please ask i will answer any questions as best i can Thanks ppl :rastasmoke:

Have you measured the ph and ppm of your runoff? If not....please do and post.

What kind of water are you using? You may be one of those whose water should be RO or distilled and some CalMag.

I'm guessing its either a ph/rockwool issue or your water. Good luck.

Hey Weedhound thnx for ur time!

Well i waterd plant today with nutrient solution at ph 5.8 then checked the run off which was ph 6.9!!
I dont have anything to test the ppm.
I used rockwool thinking it was ph stable looks like i was wrong! any quick way of helping this poor plant? The leaves from the pics above are pretty much dead now.

you need to keep your res at 5.5 becuase rockwool will naturally rise it. if you still have problems try lowering your ppm and use r.o water. also make sure you get 25% runoff. Once a week you should flush with plain water too. i usually do this while changing out my res. I like to let my res curculate for one day to balance everything out before ph balacing it. later.

use plain water for a while, sems like your burning the plants with too much food maybe

Hey guys/gals thanks for your opinions i read up on weedhounds theory and i think my tap water is the problem.
Im guessing the calcium is locking out the magnesium.
The nutrients im using already contain both, do you think it would be easier if i just use distilled water?

Thats NOt your tap water locking things out.....it's your abnormal ph. I certainly would not use RO or distilled water without using CalMag to replace lost (and NEEDED) minerals.