Aquaponic Gardening

A Community and Forum For Aquaponic Gardeners

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?

Views: 1685

Reply to This

Replies to This Discussion

Harold I think we have a start. Lettuce crops will thrive in 5.5 to 8.1 Tomatoes as high as 7.8  Squash and peppers need to be below 7.4 at least in my system. Root crops will grow as high as 7.8 . Strawberries need to be below 7.4 at least.  I am sure optimal growth on all the above depends on nitrates and trace elements available in system. This is what my system has shown so far.Corn stunted at the 7.8 but is flourishing at 7.4 on second round of plants. Broccoli is showing average growth rates at 7.8 and is fruiting.  My ph continues to fall around the 7.4 range and I am into the second round of plantings. I will keep you posted on growth rates at the lower ph.

If you are looking for a chart of what pH works best for particular types of plants, you will probably need to look to hydroponics.  They have made such charts.

 

I personally don't think those are all that useful for aquaponics though, at least not any aquaponics that is NOT monoculture.

 

Of course if you go by Hydroponic wisdom, Aquaponics doesn't work.

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.

I'm not basing my assumptions on just Nate's system.  Joel of BYAP has systems that tend to run a lower pH as well as have some of Kobus systems.  I expect that systems that run well at the lower pH are probably well managed and that the pH is not allowed to "crash" so to speak.  I have to admit that when my tower system or the 300 gallon system were cycled up and I wasn't paying close enough attention to pH that it did drop too low and then I of course had to do something about it and then it came back up to over 7 because of me adding well water since I was too busy at the time or didn't have a stock of rain water on hand to stop and get the pH settled in at a lower level and let the bacteria re-establish at the new level and get used to it.  I also happen to use the API freshwater master test kit for my pH testing so trying to hold my system at a pH of 6 would be dangerous since I can't measure below that and have no way of knowing what the pH really is if it reads 6.

 

I expect that most of the pH "crash" is probably due to the operator perhaps not paying enough attention to pH and it drops far below 6 by the time it's noticed and hence the "crash."  Ya gotta add some buffer or the bacteria run out of something they need.  I think Nate and Kobus and Joel are probably just good at observing when the plants or system "needs" something and taking care of it, thus the systems manage to tick along very nicely at the lower pH.

 

Anyway, it's all about finding the right balance.  I suppose this might be why people who want more control over things will separate the fish culture from the water pulled off for use in the plant culture so that they can more closely manipulate the pH and nutrients for the plants, unfortunately this means a loss of the water savings since it is effectively doing parallel aquaculture and hydroponics where you get to re-use your water change water from the aquaculture for the hydroponics but then when the hydroponics is done with the water it is waste and has to be discarded and the fish system is constantly getting fresh water since the plants are not in the recirculating loop.

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.

For more detail - I had the Dr Lennard calculator ratio for the amount of fish I was using, had a pH of 6.5, and ammonia close to 2 ppm at times.  Because of the low pH I never had too much dangerous un-ionized ammonia and did not loose fish.  When I started working on the alkalinity / buffering issues, the pH slowly started drifting upwards, thus I probably will not have a low pH system again when the fish come back, but in hindsight, the system was not as efficient as I would have liked it to be.  I still think we can work at increasing bacterial surface area needs for low pH systems as a bit of a safeguard.

Hi All,

We do know that whatever the nutrients in an AP system , they become bio-available only at specific PH levels. We can do what we like, but at PH 6 even if we add Iron to system water, plants are unable to absorb it unless we buffer and raise PH, or, alternately we foliar spray additive. Deficiencies actually alert us of the systems need for buffering.

Actually Iron is more available at lower pH, it is the high pH systems that have difficulty keeping Iron available to the plants.

Hi Tc,

You're right my mistake, iron is steady at 6ppm. There are others that become less available at 6ppm like phosphorus, calcium, magnesium etc. Anyway, if we have a variety of plants we do need to maintain a ball park PH. If on the other hand we grow one or two types of plants it would be good to know the average target PH specific to the nutrient demands required by these plants. This i think has already started coming out in these post, thanks to all of you.

(From Hydroponic Food Production
by Howard M. Resh
Woodbridge Press, 1987)


NOTE:
This chart is for soiless (hydroponic) gardening only and
does not apply to organic or dirt gardening.
Plant pH Range

Beans
Broccoli
Cabbage
Cantaloupe
Carrots
Chives
Cucumbers
Garlic
Lettuce
Onions
Peas
Pineapple
Pumpkin
Radish
Strawberries
Tomatoes

6.0-6.5
6.0-6.5
6.5-7.5
6.5-6.8
5.8-6.4
6.0-6.5
5.8-6.0
6.0-6.5
6.0-6.5
6.5-7.0
6.0-6.8
5.0-5.5
5.0-6.5
6.0-7.0
5.5-6.5
5.5-6.5

Hi TC,

I've had this chart myself and use it as a guide. Do you think its an accurate crossover to AP?

Probably not entirely accurate for AP since at least media bed AP is more closely related to organic gardening than Hydroponics.  But since I don't know of a chart that will tell you this same thing for AP or Organic gardening, this is a place to start.

 

Now I have to tell you that I've grown most of the above listed plants at far different pH than they seem to recommend.


Reply to Discussion

RSS

© 2020   Created by Sylvia Bernstein.   Powered by

Badges  |  Report an Issue  |  Terms of Service