Hi, this is my first post&grow. My set up is DWC a 5x25l airstone system operating under a 600 watt sodium, enclosed in a 1.2m sq Budbox.
I am in to my 3rd week of flowering, i have 3 plants left (2 have been culled). The plants are approximately 2 foot high and have begun producing an aroma. The strain is probably Thaitanic ( i started with 3 Thai and 2 Sadhu - i can't tell which is which). The root system and general plant health seem to be within acceptable parameters.
I do have some yellowing and i am compensating with nitrogen.

My problem lies with the PH rising after 1 day (or less).
*Of note*
My tap water PH falls in the range of 7.4 to 7.6 and has an EC of 0.5 to 0.6.
My tap water PH after filtering is in the range of 6.3 to 6.4 and it's EC of 0.3.
I have tried alot of permutations in order to better understand the nature of the fluctuations, of which these have been administered in a weekly fashion. So far i have tried the following:

1) Used tap water, airrated for 24 hours, brought ph down to 5.8, added nutes, transferred to growroom bucket(GB).
2) Used tap water, stirred for 40 mins, added ph down to 5.8, stirred for 40 mins, added nutes, ph 5.7, transferred to GB.
3) Used tap water, added ph down to 6.0, left for 24 hours, added nutes, ph 5.8, transferred to GB.
4) Used tap water, added ph down to 5.8, added nutes, transferred to GB.
5) Used tap water, airrated for 24 hours (to test)
6) Used tap water, (removed airstone from system) used liquid oxygen, added ph down to 5.8, added nutes, ph 5.6, transferred to GB.
7) Used tap water, (no airstone) ph down to 5.8, stirred for 40 mins, added nutes and liquid oxygen, transferred to GB
8) Used filtered tap water, (no airstone) ph down to 5.5, added nutes and liquid oxygen, transferred to GB.
9) Used filtered tap water, (no airstone) ph down to 4.7, added nutes/liquid oxygen/nitrogen[yellowing of leaves]), transferred to GB
10) Used filtered tap water, (airstone re-introduced) ph down to 5.8, added nutes/liquid oxygen/nitorgen, transferred to GB
11) Used filtered tap water, ph down to 4.4 added nutes/liquid oxygen/nitrogen, transferred to GB.

Points 5,9 and 11 have produced readings of above 7.5 after 24 hours, which does boggle me, especially 5! All of the other points also produce a PH of around 7.5 give or take 0.2, the highest i have seen it is 8.5.
Whilst i am expecting at some point this grow to die (being my first an all), it would be benefical if i had some control of the problems in which i'm facing. I have had numerous conversations regarding this with my local grow shop, and have Jorge Cervantes 'Indoor Bible'.
The PH fluctuations are defineately more apparent when i have an airstone.

Possible contributing factors are:
The air intake not being directly linked to the outside (it's enveloped in a curtain which is approximately 10 cm away from a window propped open by a bird feeder.
I smoke tobacco in the room.
PH meter out of calibration (though has been re-calibrated twice, and has always ph'd tap water within 7.5 give or take 0.1).

So any input to establish a reason for these discrepancies would be beneficial.

I am a bit confused and i wrote it

Are you ysing any bene's? Fungi/bacteria. If so, they will cause an ever increasing ph...next time cut them back to half. Using an airstone will make the ph rise as well....as you put more air in you are decreasing co2 which will make the ph go up. But you should find equilibrium after a few days. I have a good article from somewhere on the net...but can't find it at the moment...I'll get back with you

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Marijuana Defiency Guide...all the stuff now on pg 1!!http://www.rollitup.org/marijuana-pl...tml#post404474

The nutes i use as as follows:
Ionic Nutes
Liquid Oxygen (when i have it)
Liquid Nitrogen
Organo Acid

I have no Bene's as such (no funguscides)(i dont know what bene is). But above is all that i use. I dont usually add nitrogen, or at least haven't much upto this point, but occassionally as the plants need it.
The pots are designed for DWC (including lid), but there may be a chance that light can seep past the clay peebles in the net pot, also i try to leave the pots stationary and use the flap to access the water, during this time (about 5 mins) the water will be in direct line with the light source. The flap is a triangle hinged over a hole just big enough for my intrusments to access, leaving the rest of the pot in darkness.

When or if i have algae build up, i take it that will also increase PH to rise, correct?

what's bene?, i use the following :
Ionic Nutrients, Liquid Oxygen, Liquid Nitrogen (when needed) and Organo Acid only. I do get a bit of algae after 5 days sometimes. But since i replace after 7 days i have not addressed that. I do not sterlize pots inbetween, as my grow shop says i don't need to.

Bene = beneficials

What shenagen said + ph goes up as plants uptake nutes. I don't think there is anything you can do about that. In my experience, by the time the ph stops fluctuating, it's time to change the res.

What is the algea growing on?...and what's liq. oxygen...and...well I don't know whats in those products so I can't say if you've got any benefical bacteria or fungi. DEFINATELY CLEAN YOUR CONTAINERS....your grow shop is wrong. It normally is fine but it just takes that one bad one to kill a plant.

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Marijuana Defiency Guide...all the stuff now on pg 1!!http://www.rollitup.org/marijuana-pl...tml#post404474

Liquid Oxygen : For increasing oxygen content of hydroponic nutrient solution; contains Hydrogen Peroxide @ 17.5% (text as per bottle).
I get two types of stuff, 1, is the yellowy froth which after i scoop out turns into a white powder when dried. and i also get stringy like algae.
I haven't intentionally added any bene's.
Algae presence is not always, but on some occassions it has been noticeable. I have however never sterlized the containers, aside before first use. Algae mainly froths, sticks to the sides, and to a point sticks to roots, when i empty bucket there is usually either yellow froth on inner sides, and some white/grey/yellow residue on the bottom. I do wipe over with a sponge before adding next mix, but i'm not doing it with anything other than tap water. the first time i changed water about 2 months ago i did make the mistake of using washing up liquid to clean a couple of buckets, and that did result in a massive bubbly mess (haven't done that again).

OK lets see...the oxy thing sounds fine(although why don't you just get a bottle of hydr. perox.) If you are getting algea like that then you need to do some light proofing...bigtime. Also it is very important that before the next round is started you give everything a bleach cleaning. If you just wipe stuff down you will have the same issues every time. Especially with algea....if yopu leave one spec in the container it will colonize and grow as if it was never gone.(Trust me on that...I deal with that stuff on a daily basis...not in my grow) Yep don't use dish soap any moer. It sounds like you learned your lesson with it. i gota run I'll think of some more soon and find that other thing

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Marijuana Defiency Guide...all the stuff now on pg 1!!http://www.rollitup.org/marijuana-pl...tml#post404474

If you want to get the pH stable,
you will need to purchase and RO machine.

If you continue to use tapwater,
you will have mineral deficiencies,
and poor yield.

An RO machine from ebay
will solve most of your growing problems.

If you want to grow with the pros,
then you must use RO.
.

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4 inch PVC Aero with Chiller
Aero Space Shuttle
Vicious NothernBerry hempy bucket