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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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Hi TC,

This is a general guide only . I think what makes a difference is there are specific PH levels for each variety of the same type of plant. Its nonetheless good to post here, thanks. 

This discussion was borne out of the need to find a specific PH for growing root crop(David's Post), but i now suspect that this may depend on the different types of root crops as well as the different varieties of each one.

While observing the chart above I am thinking that there will never be the Ideal for AP and this is so by design. AP by nature allows the PH to fall and then have to be buffered, this way we ensure going through all the ranges for nutrient bio availability.

Hi all, 

not out drinkin yet unfortunately. . . saw some responses piling up and thought I'd reply:

on epsom salts and dolomitic lime- i put in lime only a couple times a year- it functions like a slow release pH buffer that supplements Mg which can be weird at low pHs sometimes.  Epsom salts is more of a rapid response kind of thing.  Mg will most likely not be supplied in great enough supply in most feeds- so it definitely helps- but remember that with epsom salts, a little goes a long way. . .

You guys are definitely right- my bacteria aren't at optimal pH, but my BSA is high enough that crashes are not really a problem-  I generally know what my pH is doing too, even if I'm not testing a lot- the systems are really like clocks.

I also don't feed agressively- and this is a biggie because most folks feed for the fish, but I feed for the plants- they're worth way more money than fish.  Anyway, I keep my feeding rates low with system volume high and stocking rates moderate.  This means I have enough fish to rapidly bump ammonia if I have too, but lots of system volume to buffer the effects, and not so many fish that system chem goes bad fast.

I really look for nutrient deficiencies and Mg and Fe are really the ones that turn up in my system- it'll be different for everyone depending on the source of their water, etc.  the nutrient availability charts are really guidelines- it's possible to grow at higher pHs, you just start to make the plants work harder to get nutrition, and generally limit the nutrition available.  so they will grow, but may be succeptible to certain pests or enviro. conditions. . .   anyway, i generally let my plants tell me what to do as far as system chemistry goes.  Learning to id the different deficiencies (some are hard to see) can be really useful for managing system chem.

alright, goodnight everyone, happy 4th. . .  it's time to start drinkin (you're a prophet David!).


Oh, and when raising pH always do 50-50 KOH and Hydrated lime or you'll end up with all of your potassium precipitating out. . . . this thread got long fast- i hope addressed everything brought up . . .
Boy this thread got scientific fast. If I am absorbing this right the three main supplements are Iron FE , potassium KOH and Magnesium Mg. All three are readily absorbed at the 7.0 level and absorbed to some degree at the higher 7 levels. Still not sure why Harolds root crops struggle if the charts TC posted are correct. His system should produce unless humidity and type of plant are to blame. Harold this is a great discussion.
Kobus do you think if your system was unable to handle the ammonia at the 6 range you could have slowed feeding rates way down like Nate does or lowered the fish load and the system would have functioned at a higher efficiency due to less feed imput and higher trace element absorbtion due to lower ph. I am wondering if the 6.0 range we should cut the fish to gravel ratio by half and see if the system functions correctly. I keep hearing a crash or high ammonia and cant but wonder if it is mearly the ratios are to high. I definitely will play with this on system 2.

Kobus Jooste said:
David - Without any input from Nate, I would have to guess that his system has a greater bacterial surface area to fish mass ratio than units with higher pH.  I ran my system at 20kg / 1000 liter stocking and struggled with low pH.  My component ratio (gravel) was spot on, but I could not get rid of all the ammonia.  I am now working on the assumption that this was because of reduced nitrification potential.  I will be reducing my fish load in the system when spring arrives.  I really think the ratios everyone uses is for ideal systems, and that at better or lower nitrification efficiencies, these can be adapted to result in greater or lesser midia surface area for the same fish load.

David Waite said:
TC I have to wonder about what you and Harold are discussing. Does Nates system thrive because his plants can absorb better than ours with the low ph. Obviously yes. So if his plants can absorb better he needs less of everything to include Nitrates, and trace elements. So are his stocking rates of fish per gal low enough that his bacteria at 6.0 ph can handle the ammonia and convert therefore Nate needs less of everything as an imput compared to our high ph systems. I say this because I wonder if  nitrite and nitrate bacteria live fine at the lower ph but there obviously is less of them due to the crashes that you and Harold have experienced. Maybe crash isnt the right word but you get my drift. Nate will chime in here when he quits drinkin Im sure. hehe. In final are there different strains of nitrate and nitrite bacteria that adapt to ph or are simply more at high ph of 7 than at 6. If it is the latter which I think Nate system will prove, it could be just a matter of using less fish and feed per plant and the system will function at 6.0 Be interesting to find out if a media based system that conditions its bacteria over time to 6.0 can survive and provide all the conversions and in turn grow plants with more vigor.

TCLynx said:

David, I've noticed that if the bacteria cycle up and are used to a higher pH, they will struggle and ammonia will show up as the pH drops down to 6.  However there are systems out there that have always run a fairly low pH (their well water has a low pH rather than high) and the systems cycled up used to that so they seem to manage.  Perhaps just a slightly different variety of bacteria will tend to colonize there and be suited to the conditions.


My systems all cycle up at a high pH because of my well water and when the pH drops down the bacteria will have trouble keeping up and I have to be far more careful.


Biggest trick with running a pH of 6 is that you need test equipment that will let you know if it is dropping lower than that so you can take action and keep it from dropping too low.  With the Freshwater Master test kits that most people doing aquaponics use, it is dangerous to let the pH actually get down to 6 since you can't tell if it is actually way lower.  Hence why it is recommended to take action on the pH when the pH gets down to 6.5.

Hi David,

Kobus if i remember correctly also uses a higher protein feed resulting in higher release of nitrogen and ammonia.

David - the system I had experimented with was a response to a constant Southern Africa specific question of how much food can come out of a small space.  People are incorrectly seeing AP as a conveyor belt food source to needy people pumping out fish at a daily rate.  I was trying to promote it from a plant production point of view as our soils are not always very productive and fertilizer costs are therefore high.  Water is also cronically short in supply thus AP made sense but not in the way some people were viewing it.  My experiment became a way of testing the limits of a unit in terms of stocking but also simplistic technology and using rain as an only source.  It worked once I figured it out but never as well as a similar unit I had with half the fish.


Harold is also right about the feed.  The only commercial feed I can get here has a protein count of 41% and I was feeding as much as the fish needed.  From what I am getting ooking at the thread, my initial thoughts on how Nate's system was working was in the right direction.  I am in the process of expanding my plant space, but even with 40 - 60 more plant spots in the system by spring I will not stock the same number of fish - looking at a 25% reduction.


Thanks for a good thread so far guys!!!

Hi Nate,

Thanks for this valuable tip on the combination.

Nate Storey said:

Oh, and when raising pH always do 50-50 KOH and Hydrated lime or you'll end up with all of your potassium precipitating out. . . . this thread got long fast- i hope addressed everything brought up . . .

After reading all the post, WOW really informative. Lots of things to consider for my small AP systems as its running at PH 6.0.


But also kept me thinking is that if we do not supplement a system with any nutrients can it thrive as a efficient AP system that produces good amount of greens?

It totally depends on your source water and the fish feed you use as to how much supplementing might be needed.


I know of people who say they don't supplement with any additional nutrients.


  Some places have source water that will provide much of the needed stuff and if using high quality complete fish feed designed for recirculating aquaculture, you might not need to supplement much at all.  In general for the running of many commercial systems, the pH is controlled by alternating calcium and potassium hydroxides and that takes care of both the potassium and calcium needs of the systems.  Other places where people would rather avoid the more caustic hydroxides might use calcium carbonate and alternate with potassium bicarbonate to take care of the pH while also providing the needed potassium and calcium. 


If pH is completely taken care of with the source water (like mine often is with my hard well water.) An alternate source of potassium might need to be added (usually a seaweed extract) but is most necessary in a brand new system and might not be needed once the system matures depending on the fish feed.

Iron may not need supplementing at all if the source water has some and the pH is low enough.  Chelated iron is mostly needed for systems running a pH over 7.

Teh Teong Chian said:


But also kept me thinking is that if we do not supplement a system with any nutrients can it thrive as a efficient AP system that produces good amount of greens?

low pHs are really your friend.  K doesn't always need to be added- it's mostly because most folks use hydrated lime (Calcium hydroxide; Ca(OH)2) to raise pH.  and over time, depending on how often your pH needs to be raised, the Ca from the lime makes the K in the system precipitate out of the solution.  So, if you don't have to raise pH very often, then you can probably use lime (as the calcium is consumed in system by your plants) without having to worry about K additions.  However, if you're adding lime consistently, then K additions become necessary because you're adding more calcium than the plants can often consume at a fast enough rate, and then it begins to compete with K.  There should generally be plenty of K from your feed for the production of most vegetables, but it's the addition of lime itself that leads to limited plant availbility/preciptating out.  For instance, several weeks ago I had one basil tower that began to show a mild K deficiency, so we switched over to pH raising only with KOH, and now the deficiency is gone.  There was probably enough K in the system, but it was probably a precipitate on the bottom of my tanks. . . until I raised the K concentration in the system.

Hi Nate,

This means that the calcium builds in the system as we buffer PH and over time causes potassium to precipitate out and shows as deficiency even though it was previously available?. Do you think the high calcium also reduce the bio availability of potassium even though it may be present in the water?

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