nft ph fluctuations. what could be causing this

hi everyone i have 25 plants in a diy nft channel (it is just a pice of plastic house guttering) the seeds were started in jiffy pellets and then inserted about half way into a nft plug so that the pellet is above the flowing water and just the roots are hanging in the water flow.. over the last few days the plants as a whole have started to look a bit poor.. and a few of them now look like they are going to die. after spending the last couple of days researching my symptoms i am pretty sure i have nailed it as a ph fluctuation problem.. so today i did a res change and have just refilled it with plain ph'ed water of 5.8 and within 1.5 hours it is back up to about 6.4 so i ph it down again and the cycle is repeating itself. what could be going on? sorry for the long post and thanks for looking at my post... sorry no pics yet the batterys are flat in my camera,, form is below






E-indoor or outdoor/////// indoor
E-soil, soilless, coco, aero, or hydroponic////// hydro nft
E-specific medium
CSL-Soil type/brand
HCL-Hydro/aero/soilless system type.... nft
SCL-Anything you have added to the soil
SCLR-Soil or slab runoff pH 5.8-6.4
E-Water source///// rainwater (i always use calmax)
E-Source water pH 6.3
HRT-Source water EC (if hydro)/////// dont have a meter yet
E-Age of plant////////// approx 4 wks
E-Type of fertilizer ///////// growrite (its a localy made aussie brand)
E-Rate of application (if hydro, this is your PPM number, preferably after each component is added)
E-Lighting source and distance from plant/// 1X1000w MH 1X600w lucagrow about 2.5 foot
E-Air temperature (both day and night if you are running a dark period)25-26 Day 19-22 night
HD-Reservoir temperature/// moves between 18 and 22
E-Air % Relative humidity////// 45-50%
E-Lighting schedule///// 18/6
E-Type of ventilation your room has//// 1X6" inline fan.. 2X6" pasive intakes
TR-Did you pre-soak your media in pH corrected solution?/// yes

Well....
it could be your water.....maybe go to RO or distilled with CalMag
it could be your nutes......can't say because I've never heard of them.
it could be that you aren't using ph up and down (unless you are instead of something like baking soda and vinegar to adjust your ph)
Might be those peat pellots if those are your actual medium......i think they are but 'm not quite sure.

Pictures would help a LOT!

i will get some pics up today when i get to the shop and get some batteries for my camera... the thing is i am using the same water, nutes ect in my aeroflow and dwc systems without this happening.... :wtf: anyhow i will post up the pics soon

thanks for the help weedhound.. sorry i havn't posted up pics it has been crazy around here . (3 kids and christmas.. what a combo!!) i have sorted out the problem ph is stable and the plants are looking great! :thumbsup:.. what i did is run a flush of ph,ed water h202 and calmax for 2 days the plants stared to look better after a couple of hours but on the 2nd day started to look a bit yellow. i then dumped the res and filled it with 1/2 strength nutes calmax and h202 and now they are looking better than ever... wohoo :D. the thing that has me stuffed though is this fixed the problem but what might have been causing it in the first place?

Not sure but as long as they are on the upswing that's good news!!

Good luck.

I would not be surprised if you see pH swings up again if your nutes were designed to be used in soil. Often, soil nutes are buffered to come in in the high 6's. Hydro nutes buffer in the high 5's.
Another possible cause of the swings is not changing the res often enough for the weight of the total plant material that lives off it. The greater the plant:water ratio is, the more often you have to change the whole res- DUMP and refill- to prevent nutrient imbalances and the accompanying pH issues and lockouts.

TOTALLY what she said rocks!

Learned it from your DWC adventures Weedy! :D

wohoo i think i found what was causing it... the nutes are designed for hydro so i guess they are buffered correctly.. i have been adding h202 daily and all has been great..... then i went to do my res change and found a piece of bent coat hanger that i was using to lst the plants i had in coco last grow only it was verry shiny (looked like it had been acid cleaned) so i am thinking that this could have been causing the problems... i feel like an idiot i must have droped it in when i was cleaning up...:stoned:

Ok....that was my next guess......:D