PH keeps rising
 

Hello. I recently built my own greenhouse and am sticking my toe into some hydroponics. I currently have a dozen strawberry plants and a dozen cukes and tomatoes growing. The plant are doing fine but I can not keep my ph down for the life of me. I have been running this system for about 3 weeks and every day I correct the ph to around 5.8 and every 12 hours it is back to 6.8 I am running a mixed drip/NFT (as you can see in the pics), Fox Farm Nutes, air stone and a pump. I am starting seeds in rockwool and then into hydroton. I ph adjusted the rockwool before I germinated the seeds also. I have read where people set their ph and it pretty much stays there 'till then next water change. Mine stays there for about 6 hours.... I am using spring water with a ph of 7. This isn't a big deal but I am just curious as to why my ph keeps climbing. Thanks-Scott

http://i207.photobucket.com/albums/b.../hydrocuke.jpg

http://i207.photobucket.com/albums/b.../hydrolane.jpg

pH fluctuations
 

It is important to remember that pH naturally fluctuates as the plants consume both water and nutrients at various rates over their lifecycles; consumption of water typically lowers the pH as nutrients concentrate in the solution, while consumption of nutrients typically raises the pH as the solution becomes more dilute.

In your case, since the nutrient solution consistently increases from 5.8 to 6+ on a daily basis, it sounds like your pH adjusting additive doesn't have a long buffering capacity (i.e. can't hold a solution at a desired pH for a long duration of time).

I wouldn't worry too much about it. I would only become concerned if the pH leaves the appropriate range for adequate plant growth. There is an old saying that "day traders have more heart attacks than portfolio managers," because by definition they are constantly watching the stock market fluctuations whereas portfolio managers look for longer trends; looking at the data constantly constantly can cause you headaches because sometimes the noise (natural pH fluctuations) cannot easily be distinguished from the trends (pH stability).

In other words, I wouldn't be concerned on a daily basis about the pH - it will drive you crazy trying to stabilize it, and worse, by manipulating the solution with too many additives may give you short-term victories (pH stability for a day or two) while building towards long-term problems (e.g. toxic solution or nutrient lockout).

There is also a recent thread on pH down fluctuations you might want to check out as well...

Thanks for the info. I am guilty of micromanaging! I am currently using sulfuric acid after trying PH down from a hydro store. I'll keep an eye on the ph and not try to obsess about it. :D Thanks-

millstream
Thought I would elaborate on a couple points. First is, that larger volumes of water fluctuate slower. I call it buffer water. Not that the water itself buffers anything, but the larger the volume of water is, the slower the fluctuations take place as the plants take up water and nutrients. Thus buffering against the natural fluctuations through volume. That's the main reason I always try and use at least twice the minimum recommended volume of water for the plants grown. Not such an problem while the plants are small, but it makes a big difference as they get bigger.

Second thought is I'm not sure how stable the sulfuric acid is. You may try going back to using the normal hydroponic pH adjusters, and seeing if that has any effect. I use the dry adjusters because they are much cheaper than the liquid ones (which is mostly just water anyway).