muisture, ph or what???

hi,

this is my third grow. my last one was of 8 female master kush and all went fine. i am now in a new location and my grow is going sideways.
info:
soil grow (potting soil ph6.5 with some mixed nutes) mixed with puffed clay (good drainage), 10 litre pots, 2 hps agro (400W + 600W) in cool tube about 3/4 foot above plant canopy. very large exhaust fan blowing air our via cooltube and pulling air from outside+inside (via vents in door) on during light cycle only. a tower fan blowing air across the plants 24/7. grow room is in the basement level. temp is at 21C but humidity is at 80-90%. (i plan to get a dehumidifier next week) my water (own well) measures pH 5 on lab pH test strips (4 colore indicator type).

the plants:
10 master kush female from fem seeds (nirvana)
5 raspberry caugh female from fem seeds (nirvana)
5 northern lights female from fem seeds (nirvana)
5 venus fly trap female from fem seeds (nirvana)

all plants are into week 3 of veg light cycle is 18/6. no nutrients given yet.

here are some pics and sorry for the HPS being on!



all of the master kush are doing badly. drooping down claw like badly. some more then others. the raspberry cough and the venus fly trap are doing well (some small yellow spots but i'm not yet worried about them!) but the northern lights are showing some signs of drooping too.
i watered them by accident with ph5 water 2 times before i tested the water. since then they had one watering balanced with baking soda to ph 7. (i have ordered pH down base) i tried to mesur soil ph but coult not tell for sure (between pH 5 and 6.5)
it is definitlly not over watering! i test with a moisture probe and let them dry out almost totally before every plant gets watered.
what can it be? PH? moisture? venting (due to basement conditions)?
some are very bad. the third pic from the left is the worst master kush.
i did my due diligence and read all of the articles but no definitive answer found. and they do say a picture is worth a thousand words....
and one have an idea whats wrong?
thanks guys...

are they getting enough water m8? what about fresh air ? that many plants will need a lot of each. when did you notice it first? maybe you need to start small feeds, ph should be 6.5 but you know this ,fuck knows m8 but i will keep thinking . i hope this gets sorted yer poor wee plants, ma heart bleeds fur ye.

water i give when needed (almost dry) it has been about once a week till now. i was a bit surprised about how little water they need but i check each pot with a soil moisture probe so.... air exchange is good and if any thing the fan is over sized (it's a industrial exhaust fan for venting crawl spaces under homes). i don't know about air quality being that its a basement. out side and basement humidity is high so although there is good air exchange the air is very humid!

i would have said over watered but, have to go for your soil mate imho. not sure though,

ya, i will have to get a soil pH meter... i was also thinking that because of high humidity (high 80's) it may have "over water" symptoms due to the fact it can't evaporate moisture well via it's leaves. the temps were also slightly on the low side (21C/69.8F) so i placed a heater last night in the room and the temp is now stable at 24C/75F and RH is a bit better at 75%. as i said i will buy a dehumidifier next week. i also set the exhaust vents that were on only during light hours to run 24/7. i hope that would help.

thanks for the comments. any other ideas? what can be effecting the master kush plants more the the others?

p.s. i also clipped them and took the lower branches for cloning 4 days ego so they might not show signs of recovery so fast...