Newbe dwc problems

Hi guys, great site been looking about on here for a while in preperation and for general info. I'm doing my first rdwc after doing 6/7 problem free soil grows. I took some time out and then decided to give the dwc a bash for a change , I'm in the uk so mums the word .
To be honest it's not been a great experience so far really or I'm just expecting too much I'm not sure.
I have 5 20l buckets inside the 2x2x2m tent 1x 20l Rez outside tent ,top fed system.4" air stones in each bucket and substantial air pumps .1x600w hps about 2ft above grow ,6" carbon outlet with 4" inlet, large 12" oscillating fan, temps 65/70 lights off 70/80 lights on. I did a lot of research and spared no cost so far, using canna nutes A+B.
I'm growing ww x bb and I germinated them in 1" rockwool .then after roots showed I inserted them into the 4" cubes and it's been 3 weeks now in the dwc in 6" pots.
5 plants all looking like various states of growth from 2"-6" tall , 2 plants looking small & stunted , various brown/yellow spots on older leaves , one looks droopy etc etc. from day 1 the ph is a rock solid 5.8 once set and tbh never moves all week as we speak the ppm is around 550 again never moves really , tbh I don't rarely have to do much . And this is all buckets all perfect spot on and checked twice a day . I've flushed twice also . The roots are amazing on 4/5 , the other 1 not so good like 2/3 long roots in the water. They are pearly white in colour also.i feel like I'm doing everything by the book but the results are very hit and miss considering they are all in the same medium.
These are problems I've been fighting with since week one: leaf claw/deformation , yellow spots on older/lower fan leaves, lower leaves browning, curling/drooping down like it's been over watered, stunted growth.
Now I'm at the conclusion that maybe 550 ppm may be to much to soon and causing a lockout of some sort , nitrogen toxicity possibly , I just don't no I'm stabbing in the dark really , trial n error n all that. But was thinking of dumping the whole water and filling with ph'd plain water for a few days and go from there , so just wondered if anyone else can see something I'm missing , any ideas appreciated in advance.

Sounds like your right on with it.

I've had something similar to your experience during my current attempt at a simple dwc. I replaced the nutrients with ph`d water and added h2o2 and ran it for 8 hours. Then re-ran it with a fresh nute solution at the same ppm. 900 I believe .
The plant turned the corner and has been doing fine for the last 2 weeks... Knock on wood.

Good luck to ya.

"let it be"

I would say you started the nutes to high to soon. I started my nutrients at about 250ppm in the first few weeks then I tried to jump it up to 500 by week 3, I had huge issues with all my roots going brown (burnt them), overwatering issues and same sort of problems as you have had. I corrected the nutrients to a much lower schedule and the roots have mostly recovered, plant growth has been much better with new roots forming from browned roots.

Key to hydro depending on your strain is jus read the plant as you grow, just like soil. Start slow on the nutrient levels and only increase them gradually over time. A good way to do it is have your 250ppm to start then just adjust the PH, don't add more nutrients directly to the res. At 10 days you will find many of the nutrients still in the water as the plants do not have the ability to always uptake a full regiment of nutes, some more than others. Empty res and start over with a 350 solution, making sure you adjusted PH of water first before adding nutrients. Just step it up like this bit by bit. My plants are only at about 400ppm now, although I add 10ml A+B every 3 days to boost it back up to about 500ppm, then once every 10 days empty 3/4 reservoir, fill with plain water and do a 15min flush before dumping all the water and starting over with +50-150 more ppm. As long as there is growth and no deficiencies less is more.

I have been trying hydro also and my plants are a few days away until a month from seed, they are doing really well and I will be switching them to flower after about another week.

Cool I hear you guys , problem here is I use tap water so my baseline is 300 ppm give or take , I don't really want to start doing fancy stuff to my water

Also as my roots are looking good and healthy h202 is maybe a bit overkill, so would normal phd water for a few day etc free up the plant from any lockout?

Should do fine without the h2o2. I used it to kill any unwanted bacteria that may have invaded the root zone.

"Let it be"

I never used H202, I just brew beneficial tea, helps the roots intake nutrients instead of hurting them plus stops any root slime. One cup in 5 gallons, once a week keeps the slime away.