Understanding why your PH does what it does...

When water reacts with itself to create the H3O(+)(hydroxyl) and OH(-) (hydroxide) species, one of the most fundamental and important characteristics of aqueous solutions is generated. The reactivity of a solution and its interaction with living organisms is determined in a great extent by the concentration of these two species, a variable usually measured as pH which is nothing but the negative value of the logarithm of the concentration of the H3O(+) ion. In hydroponic culture – where our plants are in great contact with aqueous solutions – the understanding of the role of the H3O(+) and OH(-) ions and their measurement as pH becomes very important if an in-depth understanding of what is going on wants to be attained. On today’s post I will attempt to guide you into this micro world of pH and how and why pH changes within a hydroponic crop. What determines pH ? This variable is inversely proportional to the concentration of H3O(+) ions and directly proportional to OH(-) ions, the more hydroxil ions you have the more acidic your solution will be (the lower the pH) while more hydroxide ions will increase your pH and give you a higher pH reading. It is important to understand here that hydroxyl and hydroxide ions determine each other’s concentration. Since water’s self-reaction equilibria must be maintained, the sum of pH and pOH must always be equal to 14 (a neat consequence of chemical equilibrium theory). When the concentration of hydroxyl and hydroxide ions is equal, pH and pOH contribute equally to the solution and they are therefore both 7, reason why the pH of a neutral solution has this value. Now that we know a little bit about pH we can understand better what happens when plants interact with a nutrient solution. When a plant is put within a given solution it wants to absorb the nutrients it needs to grow. These nutrients are available as ions that have a given charge. For example, nitrogen is absorbed as the nitrate ion (NO3(-)) while potassium is absorbed as the K(+) ion. When a plant takes potassium in, it deplets the solution of a positive charge. Since the solution must remain neutral the plant gives the solution an H3O(+) ion to compensate. The plant has therefore decreased the pH of the solution by absorbing a potassium ion. When nitrate is absorbed – an ion with a negative charge- the plant does the opposite and exchanges the nitrate for an OH(-), the pH of the solution is increased.
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If plants absorbed nutrients in a perfectly symmetrical fashion, they would not increase or decrease pH as overall charge changes would be compensated. However – as no one is perfect- plants absorb nutrients at different rates and they therefore create a “pull” towards a certain pH region. If a plant absorbs nitrate heavily it will start to contribute far more OH(-) than H3O(+) ions into the solution and the result will be a net increase in pH. Depending on the composition of the nutrients and the overall growth stage of the plant, different net movements in pH can be achieved by the plant.
The most influential factor in the changes of pH within a solution is generally the composition of the nitrogen component of the solution. When plants absorb ammonium ions NH4(+) they tend to decrease pH while nitrate – as mentioned above – tends to increase pH when absorbed. If you contribute a percentage of the nitrogen in your solution as ammonia the net effect will be a beneficial “absorption pH buffer” since plants will take nitrogen in both forms, effectively delaying the onset of important pH variations. Of course, the ratio of nutrients also performs a vital role since plants’ nutrient absorption mechanism are largely non-specific and they are greatly influenced by the different concentrations of nutrients within the solutions. Having a nutrient solution designed to provide an adequate balance will be vital in helping you control pH fluctuations.

Great first post. +rep for ya.
Learned a couple things

i second that.

Impressive ... Welcome to RIU by the way...

Thank you...Dropped by a friends house today, noticed a plant in his system that was basically dying. After talking for awhile he finally said the only thing different about the environment this plant was in was a copper or brass fitting he had tied to his airstone hose to hold it down, the other 3 plants had fish weights(lead). I just walked over, lifted the lid, and clipped of the zip tie holding the copper fitting and handed it to him. Not a good idea. Both copper, and brass(which is copper with zinc added) react badly with water and oxygen(airstone). Copper for example, releases copper oxide into oxygen. So what do you think that was doing to my friends plant via the airstone. Brass releases that and zinc ions, which interfere with hydroxide ions and cause the PH to drift up. Anything used in constructing a hydroponic system should be inert, even the silly stuff like an airstone weight. I personally wouldn't use a lead fish weight either, but thats my opinion. I could write all day about reactions, just know that even the smallest thing can cause a huge reaction in water and oxygen.

Post #2 is win as well. You are on a roll.

Mr. H2O said:

Thank you...Dropped by a friends house today, noticed a plant in his system that was basically dying. After talking for awhile he finally said the only thing different about the environment this plant was in was a copper or brass fitting he had tied to his airstone hose to hold it down, the other 3 plants had fish weights(lead). I just walked over, lifted the lid, and clipped of the zip tie holding the copper fitting and handed it to him. Not a good idea. Both copper, and brass(which is copper with zinc added) react badly with water and oxygen(airstone). Copper for example, releases copper oxide into oxygen. So what do you think that was doing to my friends plant via the airstone. Brass releases that and zinc ions, which interfere with hydroxide ions and cause the PH to drift up. Anything used in constructing a hydroponic system should be inert, even the silly stuff like an airstone weight. I personally wouldn't use a lead fish weight either, but thats my opinion. I could write all day about reactions, just know that even the smallest thing can cause a huge reaction in water and oxygen.

Click to expand...

Although PH is important in hydroponics, it basically takes a back seat to more important things, such as PPM or EC, and nutrient mix. Basically, the mix is how you control the PH, not the other way around. I have found that alot of the plant problems growers are having on this site are due to mix problems, or not changing a reservoir every 7-10 days, and not understanding that the jump from 5.8 to 6.1 is a reaction to a change in the mix. I'm in 20 gallons, and I change mine every 10 days, as well as flush each plant. Larger reservoirs can go longer, but if you're in a waterfarm, 7 days and I'd flush and change, regardless.
Also, people need to realize this, every strain is different, one seedbank plant may be good at 5.8, while bag seed tends to want to be in the 6.1-6.8 range. If you look at any PH chart floating around you will notice a section from 6.1 to 6.9 conveniently missing. This leads alot to exercise a heavy hand with the PH tools, and hurting things in the long run thinking 5.5 to 6.1 is the limit. Put the mix first, read all you can, and soon you'll be growing like a pro. Once you gain an understanding of the mix, the PH will tell you what is going on. Simple as that.
I'm legal, old, and retired from the waste water industry. PH, chlorine, BOD, all part of my career. When you would flush, I cleaned it and gave it back to nature. My advice, a good log book, and put the PH meter away for a sec and concentrate on your mix.

Mr. H2O said:

Thank you...Dropped by a friends house today, noticed a plant in his system that was basically dying. After talking for awhile he finally said the only thing different about the environment this plant was in was a copper or brass fitting he had tied to his airstone hose to hold it down, the other 3 plants had fish weights(lead). I just walked over, lifted the lid, and clipped of the zip tie holding the copper fitting and handed it to him. Not a good idea. Both copper, and brass(which is copper with zinc added) react badly with water and oxygen(airstone). Copper for example, releases copper oxide into oxygen. So what do you think that was doing to my friends plant via the airstone. Brass releases that and zinc ions, which interfere with hydroxide ions and cause the PH to drift up. Anything used in constructing a hydroponic system should be inert, even the silly stuff like an airstone weight. I personally wouldn't use a lead fish weight either, but thats my opinion. I could write all day about reactions, just know that even the smallest thing can cause a huge reaction in water and oxygen.

Click to expand...

Mr. H2O said:

Although PH is important in hydroponics, it basically takes a back seat to more important things, such as PPM or EC, and nutrient mix. Basically, the mix is how you control the PH, not the other way around. I have found that alot of the plant problems growers are having on this site are due to mix problems, or not changing a reservoir every 7-10 days, and not understanding that the jump from 5.8 to 6.1 is a reaction to a change in the mix. I'm in 20 gallons, and I change mine every 10 days, as well as flush each plant. Larger reservoirs can go longer, but if you're in a waterfarm, 7 days and I'd flush and change, regardless.
Also, people need to realize this, every strain is different, one seedbank plant may be good at 5.8, while bag seed tends to want to be in the 6.1-6.8 range. If you look at any PH chart floating around you will notice a section from 6.1 to 6.9 conveniently missing. This leads alot to exercise a heavy hand with the PH tools, and hurting things in the log run thinking 5.5 to 6.1 is the limit. Put the mix first, read all you can, and soon you'll be growing like a pro. Once you gain an understanding of the mix, the PH will tell you what is going on. Simple as that.
I'm legal, old, and retired from the waste water industry. PH, chlorine, BOD, all part of my career. When you would flush, I cleaned it and gave it back to nature. My advice, a good log book, and put the PH meter away for a sec and concentrate on your mix.

Click to expand...

RawBudzski said:

Post #2 is win as well. You are on a roll.

Click to expand...

Wooo HUU HUU. Not only is post #2 a win but post #3 struck my fancy as well
Andddd.......... ANOTHER +REP for you there fine sir.

Most water companies use something other the pure chlorine, mine uses chlorine on the wastewater side, and chloromine at the water plant. Good luck waiting for chloromine to evaporate. It will happen, but not in 24 hours, more like a week. PetSmart has a de-chlorifying solution, and yes it works. They also sell hydroton, but it's located in the Lizard section, FYI. Tap, in my opinion, is OK as long as the PPM is below 100, anything a fish can live in, is ok for plants. R/O systems are awesome, if you have the money, get one. I simply use the drops, my PPM's are below 50 PPM to start, and my plants are huge. Warning, do not get de-chlorifier that adds a slime layer, breeds algae, and you don't want that.
Think about it like this, if you owned a large company that catered to hydro users, and disinformation boosted your sales, what would you do as a CEO. Wish I owned a R/O company right now. Don't think I'm dogging on the R/O companies, the systems work, and some of us need them. My point is, if you have a low PPM already, don't lose your mind, Petsmart is an option.
Don't just ignore it, chlorine will retard your growth every time you intoduce it into your system. Deal with it.
You can do a simple search online for the analysis of your local water, just remember, between you and your source, lies a large amount of pipe, and it's all full of corrosion and deposits. So take the results with a grain of salt. I did an analysis, and mine is fine.
So, chlorine, isn't as bad as most make it out, it will turn your tips yellow, and slow things down a bit, but won't kill your plant. It's up to you how you deal...

Mr. H2O said:

Although PH is important in hydroponics, it basically takes a back seat to more important things, such as PPM or EC, and nutrient mix. Basically, the mix is how you control the PH, not the other way around. I have found that alot of the plant problems growers are having on this site are due to mix problems, or not changing a reservoir every 7-10 days, and not understanding that the jump from 5.8 to 6.1 is a reaction to a change in the mix. I'm in 20 gallons, and I change mine every 10 days, as well as flush each plant. Larger reservoirs can go longer, but if you're in a waterfarm, 7 days and I'd flush and change, regardless.
Also, people need to realize this, every strain is different, one seedbank plant may be good at 5.8, while bag seed tends to want to be in the 6.1-6.8 range. If you look at any PH chart floating around you will notice a section from 6.1 to 6.9 conveniently missing. This leads alot to exercise a heavy hand with the PH tools, and hurting things in the log run thinking 5.5 to 6.1 is the limit. Put the mix first, read all you can, and soon you'll be growing like a pro. Once you gain an understanding of the mix, the PH will tell you what is going on. Simple as that.
I'm legal, old, and retired from the waste water industry. PH, chlorine, BOD, all part of my career. When you would flush, I cleaned it and gave it back to nature. My advice, a good log book, and put the PH meter away for a sec and concentrate on your mix.

Click to expand...

so glad to hear you say that since i tell that to people also. I only do cuz i dont test mine and def dont know all that other info. Very nice post, thanks!