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Hi All,

In another discussion, some of us are trying to determine the ranges of PH for best growth of different crop grown. This can become a general guide for maintaining specific PH levels to suit the crop you choose to grow.

So, what is your average system PH and what plant (plant doing the best) do you notice thriving at this PH level?

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That's right Harold.  But again, it depends on how much lime addition you're doing.  If you're liming at a low rate (slow pH drop) then your Ca can be removed from the system by your plants.  If it starts to build up however, you get limited K availability, even if there's lots of K in your system.  Basically, it's still there, it's just not plant available.  That's why it's really important to incorporate KOH or Kbicarb into your system pH raising regime.

Hi Nate,

Thanks for the Information Nate. On this topic we see how PH can cause lockout of certain macro-nutrients even though they are available in system water. What's interesting to note here is that as we routinely buffer PH with Lime, for instance, as is necessary in AP, over time a build up or an over abundance of one nutrient can create a "lockout" of another nutrient and display symptoms of deficiency which can be misdiagnosed by the operator as a PH problem.

In your experience Nate, how do you recommend alternating dosing between lime and KOH ?

That's exactly right Harold.  Moreover, the lack of certain elements can cause increased uptake of others, causing toxicity at times.  For instance, a lack of plant available K can increase uptake of Fe, possibly causing Fe toxicity, or causing Fe deficiency if all the system Fe is consumed.  It can be tricky deciphering what your plants are trying to tell you.


We typically do 50% Ca(OH)2 and 50% KOH for our pH raising.  This is because we add a base every day to our system.  With this amount of addition, Ca can build up and cause our K deficiency, which in turn can increase Fe consumption, which can lead to Fe deficiency- your system nutrition can really be a house of cards, and unless you can recognize the deficiency and respond, you end up with problems.  But this is not likely something beginning AP enthusiats will run into (I don't want to scare anyone!)- it mostly become a problem in mature systems with consistently dropping pH.


I recommend using lime until you begin to notice K deficiency (often bronzing of plant leaves, or purple flecking or margins on leaves), respond by switching to KOH for a couple weeks- deficiency symptoms should disappear within a week to week and a half.  If you go this route- if it never becomes a problem, you never have to deal with it.  If you're going commercial though, KOH additions on a regular basis are a must for Ca/K ion balance.

Hi Nate,

Recently( 2 mths ago)plants in my AP were showing signs of Potassium deficiency and later exhibiting high iron uptake(especially lettuce), how i dealt with it was with water exchange which is not ideal as it just throwing away hard earned nutrient. I had been adding mono potassium at the time but from your explanation, when the time comes again I'll know to go the route of using the hydroxide.


I hate to push you but I as am no expert at water chemistry(really a big dummy), do you know what happens with plant uptake of nitrates when the system has this type of chemical lockout?


BTW thanks for you know what!

Nitrate availability isn't really impacted too much by other nutrients, but can be impacted by the addition of nutrients changing your biology- for instance, if you were to add a phosphate of some kind you might cause an algal bloom which could crash your nitrates. . . something like that.  by and large though, nitrates are pretty independent as far as availability goes.  Really the things that impact nitrate consumption are primarily deficiencies of other nutrients- these would be limiting nutrients.  you need to watch adding high carbon stuff too- i.e. peat or some other high carbon, low nitrogen organic matter- this will consume your nitrates in the decomposition process because it takes nitrogen to break it down.
Super info Nate!
Any ideas that might help a system with way much calcium in it?  As in a system being topped up with calcium carbonate rich well water out of a limestone aquifer?  I notice with one of my systems the pH doesn't come down during the dry season when I don't have enough rain water to keep it topped up that way.  If the pH is staying at 7.4-7.6 it isn't like I need to add any KOH to keep the pH up, what might some one do to avoid the calcium locking up the potassium in this case any ideas?
Well, there are some ways of dealing with this problem in soils, but they primarily have to do with supplementing locked out nutrients that high Ca causes. . . .  I think that if you're forced to consistently use carbonate rich water, you're kind of stuck, honestly.  you might just have to look for deficiencies and do foliar nutrient applications if a something arises.  It really just depends on the amount of carbonate that's built up in your system over the years.  if your pH is 7.4, I think you're winning the battle, and if it stays around 7.4 you shouldn't have too many nutrient availbility issues, but with lots of Ca you'll definitely have solubility/lockout issues. . . Hmm.  I just don't see a solution without reducing the amount of well water you use in favor of rainwater. . . .but again this might not be feasible.  I do know they make small aquarium sized RO filters for fairly cheap now.  You might be able to use one intermittently to reduce your use of well water to the point where your in-system carbonates can be consumed, dropping your pH, and for removal of Ca.  That's really the only option I see. . . All of my systems are on RO now, and it's really made my life so much easier.

Hi Nate/TC,

TC;     High PH and Calcium from source water, wow!. AP is adaptable to almost any environment in the world, lucky us! For me personally, I'd capitalize on rain water catchment. At least you do have adequate rainfall and if you can store enough of it for water replenishment over the seasons....... Of course its an investment but necessary to get your AP to adapt to your geography.

Nate;      I think RO strips everything from the water? In this case do you depend on foliar spray as your main source of   nutrient supplementation? Or do you use it up to a certain point.

I use RO only to top the system off.  all of my input water is RO.  Once it's in-system it's free and clear!  All you really want to use RO for is to treat your source water to remove carbonates (especially) and make your system chemistry a little easier to work with.

Hi Nate,

I think its a great idea. That's what i wanted to do by topping off with rain water(demineralized ) but after a while you get the PH plunge effect. I thought this would allow me to micromanage the nutrients in the water to find what's more suitable for individual plants. Eventually i reverted to topping with degassed pipe water. Is this the reason your system PH remains so low, because the replacement water has very little nutrient? 

Hi Harold,

Yes.  While source water can deliver some nutrients to your system, relying on source water for nutrition is just not worth it.  All of the plant nutrients you need can be found in your system with proper feeding and pH management.  My pH is low primarily because my nitrifying bacteria are really happy and I have almost no carbonates in my system because I use RO water as source water.  Basically, getting the carbonates out allows me to tightly control pH instead of loosely managing it.  It makes for a much more stress free life.  :)

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