PH Level and Crop?

[Harold Sukhbir]

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?

[Harold Sukhbir]

My system has a PH between 6.8 and 7 ppm. The plant doing best are tomatoes.

 

[TCLynx]

Big system, pH generally around 7.6 (this will vary some based on season and top up water, has been as low as 7.1 in rainy season when pushing the bio-filter and high as 8 when adding a huge amount of well water when doing major system changes like adding the new fish tank.)  Best plant growth has been Watercress this past winter (water cress loves alkali water apparently.)  However I've also done great with leaf lettuce, basil, water chestnuts, tomatoes, bananas, purslane, broccoli, collards, turnips, kale, swiss chard, carrots, and many other things.  I have not done well with cucumbers, squash or any of the related plants in this system.

 

The 300 gallon system.  When topping up with well water the pH stays around 7.6 but now that the rains are back the pH is down to 7.2 and hopefully will get down into the 6.8-7.0 range soon.  Tomatoes and corn are doing well now.  Over winter the broccoli and beets did great.

 

The tower system pH tends to drop more easily but that system isn't appropriate for as wide a range of plants.  Basil, swiss chard, plantain (yea the lawn weed), nasturtium, stevia, parsley, and purslane all doing well.

[David Waite]

Harold in the beginning my system was at 7.8 for 3 months. During that time my tomatoes lettuce crops, onions, garlic all thrived. The only thing that failed was peppers, squash pumpkin, and strawberries oh yea and corn. My system has been dropping to 7.4 and now all the above are starting to grow. I am also just started adding a iron mangnesium and zinc supplement. I will keep You posted.

[Nate Storey]

Almost all plants will be happiest between 5.5 and 7.0.  With most of these happiest between 5.5 and 6.5. . .  lettuce will like 6.5-7, but almost everything else really likes it below 6.5.  It's almost always has to do with nutrient availability.  If your system pH is between 6.2 and 6.7 you're in good shape.  My pH consistently stays around 6.0 and I'm always trying to raise it, but I seldom have nutrient deficiencies and I usually beat most season requirements on the stuff I grow. . . 

I use KOH and hydrated lime to raise pH, supplement Chel. Fe, and occasionally supplement with epsom salts and dolomitic lime (Mg once a year maybe. . . if I even see the slightest leaf curl.). . . so I guess I don't usually have nutrient deficiencies- an ounce of prevention and all that. 

[David Waite]

Nate you mentioned dolomitic lime  and epsom salts for leaf curl. I have these deficiencys in my tomatoes. Can you elaborate on how much and how often. How are your tilapia handling the 6.0 ph. It is really interesting that you are running a full point below what is considered the base and your bacteria are thriving. You really have the nutrient balance down to a science. I think your verticle operation will eventually compete with rafts in the commercial setting in aquaponics.

Nate Storey said:

Almost all plants will be happiest between 5.5 and 7.0.  With most of these happiest between 5.5 and 6.5. . .  lettuce will like 6.5-7, but almost everything else really likes it below 6.5.  It's almost always has to do with nutrient availability.  If your system pH is between 6.2 and 6.7 you're in good shape.  My pH consistently stays around 6.0 and I'm always trying to raise it, but I seldom have nutrient deficiencies and I usually beat most season requirements on the stuff I grow. . . 

I use KOH and hydrated lime to raise pH, supplement Chel. Fe, and occasionally supplement with epsom salts and dolomitic lime (Mg once a year maybe. . . if I even see the slightest leaf curl.). . . so I guess I don't usually have nutrient deficiencies- an ounce of prevention and all that. 

[TCLynx]

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.

[Harold Sukhbir]

Hi TC,

Great points all. I've noticed there are very few AP'ers dedicated to experimenting and pushing the limits of AP to get a better understanding of holistic AP. The few I've seen on this site are really the pioneers of modern AP who will carry the science forward to a world waiting patiently(even if they don't know it as yet). From these few post, these few short lines, (David, Nate, Yourself) there is tremendous knowledge which is useful for anyone practicing AP.

There is one problem I've encountered along the way with a low PH. The bacteria multiplies during cycling at a nominally high PH and resides into a fixed colony as the PH naturally drops.Trick is maintaining this population. We have available here locally manufactured fish feed(aquaculture type) which is approx. 1/3 the cost of the average tilapia feed.So naturally I started some trials on my system at low 6.2 PH( about 7-8 months already established). The bacteria crashed about 5 times, and each time i had to mini cycle and stop feeding which i did by raising PH up around 7. I did this 5 times only due to the attractive cost of the local feed and it was my hope that some resistant bacterial strain might establish itself. I was assured by the manufacturer that there were no antibiotics present in the feed, but i believe it contained hormones in the fillers, which were inhibiting/destroying bacterial growth. I have since reverted to the imported feed and the system stabilized but remain cautious and not maintain a 6.8-7 PH. If something goes wrong and you're at 6ppm PH you can lose everything at 7ppm you can recover more quickly

 

[Kobus Jooste]

Harold, perhaps I have a different approach, but I am working on a slightly different approach. I have built three systems, and they all seemed to stabilize at a different pH in the end.  I find it easier to wait for this point to show up, and then try to work with it.  The exception to this being the time that I decided to start looking for an alkalinity substitute for my rain water system.  If we consider the posts above, then the theory is that the bacteria, fish and plants all have a roughly happy opportunity to do allright in a range from 6.5 to 7.8.  My approach is therefore to see where the system wants to be and then work with that.  If a plant is not happy, it can go live in the compost bin.  Perhaps I am taking too little interest in the finer intricacies of pH, but I do not wish to battle a system constantly to get to a pH within my "happy range".  I have done this before and it was not worth it for me.

 

For me, the pH of a unit is the sum of all the parts - the water, the media, the containers, the feed and the plants.  I think each stabilizes where it wants to be and then we work with that.  Perhaps also add some alkalinity buffer agents to the line above. 

[David Waite]

I like you Harold am a curios person by nature. I find systems like Nates very intriguing. He is doing something very different hence he is probably the leader in the industry in verticle aquaponics systems. His low ph is way better for plants and apparantly a little risky for you and TC. My water science while improving is way under all three of you. I will stay within the parameters for a while but can see myself pushing things like ph and nitrates in my next system. Great info.

[TCLynx]

I like Kobus method of finding where a system tends to balance out and working with it.  And I agree with the last sentence that some buffering some how or other is probably needed (my case the well water tends to take care of it or my shells.)

 

One of the biggest issues is when you make a major change and then you have to find the new balance.  I got some friends who switched from using city water to collecting and using rain water and when they first made that switch, they didn't know anything about buffering, water hardness, alkalinity and they had a pH crash and to re-cycle and a bunch of that.

 

Now I expect it's possible to take a system that cycles up and a higher pH and slowly over time get the pH down to a lower level but that will take very careful monitoring and not letting the pH drop too suddenly and depending on so many things, if it is a huge struggle to maintain the pH at some level different than it tends to want to be then it is probably not worth the extra effort.  Friendlies uses coral sand to buffer their system pH and their system seems to settle in at the low 7 range, it works for them so they don't fight it.

 

I'm still trying to find the balance for my tower system but I think I'm gonna be able to balance that one at a lower pH then my other systems.

 

The big system of course has a high pH due to shells as a big portion of the media, some plants just don't like it while others do just fine and getting better every year, Watercress LOVEs it.

 

The 300 gallon system seems to be settling in between the two now that it is getting a bit of maturity on it.  This will change when I get the rain water collection installed and I'll probably need to pay more attention to the buffering on this one.

[Harold Sukhbir]

Hi All,

Off course we inevitably will all have to work with the specific system induced PH's. What I was hoping for in the post is to document the close to ideal PH ranges for specific plants, in that way the operator can set out knowing beforehand his PH target, especially for mono culture or for commercial application. I am aware that there are other variables to consider but trying to quantifying PH/plants in more specific terms. In these types of culture, knowledge of PH will be an advantage to greater efficiency.

Nates verticals are a marvelous addition and IMO offer unparalleled air/water interface in AP. I'm not sure, but I do suspect will offer greater ammonia conversion than most other conventional media( going by his recommended ratios )........hence a declining and low PH. May be Nate can lean in here on this.

[Kobus Jooste]

Harold - I think that if you truly want to get to the bottom of this, you will have to break your question down into three components:

1) The nutrients in your system (food, additives, chemical process releases)

2) The specific availability of these nutrients at your specific or preferred pH

3) The influence that the results of point 2 will have on the desired or ideal crops for your system.

Harold Sukhbir said:

Hi All,

Off course we inevitably will all have to work with the specific system induced PH's. What I was hoping for in the post is to document the close to ideal PH ranges for specific plants, in that way the operator can set out knowing beforehand his PH target, especially for mono culture or for commercial application. I am aware that there are other variables to consider but trying to quantifying PH/plants in more specific terms. In these types of culture, knowledge of PH will be an advantage to greater efficiency.

Nates verticals are a marvelous addition and IMO offer unparalleled air/water interface in AP. I'm not sure, but I do suspect will offer greater ammonia conversion than most other conventional media( going by his recommended ratios )........hence a declining and low PH. May be Nate can lean in here on this.