I wanted to know what are the veriables that cause ph to change. I am using an aeroponices system and find my self adding ph down every day. I am using fox farm organic ph down.

Weather I do beleive plays a role in it, I have noticed when summer came on the P.h. would really flux day by day. Even though it is a weather controlled room. Oh I also was useing fox farm nutes. And I always will.

plants do give off waste on top of an intake of nutrients. you're adding and removing things from the water which can and will cause a fluctuation in pH. it's best to check your pH every day if you can but at least a couple times a week. remember you always do this AFTER you add your nutrients and additives....as well as if you're using a reservoir you keep filled and using for 1-2 weeks and you're adding some nutrients every few days to keep up the concentration.

alkalinity is a measure of waters ability to nutralize acids and will change the rate of fluctation(cant spell). so higher alk= less change in pH to than lower alk water exposed to the same conditions. Do not confuse higher alk with meaning more alkline ( higher pH) pH and alkalinity are different. Dont know if this helps, and shit, dont even know the suggested alklinity for areo growing, but i would deff take your water to a pool store and if its a good one they will test your water and tell yor the alk... just act like its your pool water. they also have test strips so you could test it at home.

i concur with stickyicky, i have read here a few times about plant waste effecting PH....spot on sticky

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It's the ions in the nutrients
they allways wanna be nuetral so your Ph rises.
when your add ph down you add Negative ions and it drops the Ph.
(in a Nut Shell) and the cycle starts all over again.

The kind of water you use has alot to do with it too
as to how fast your Ph rises back to nuetral or higher if your
using tap water compared to distilled or RO

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I had this sort of problem and I stopped the organics and started using h2o2 and the ph stabilized immediately.

I X4 the size of my res and the issue is nonexistent.

does PH down make ur water more acidic or alkaline based?

More Acidic.

> 7.0 = Alkaline
< 7.0 = Acid