Murray

EC = Electrical Conductivity

49 posts in this topic

Electrical Conductivity is a good way to measure the nutrient concentration in your Aquaponics System. That is a measure of the water borne nutrients available to the plants. It should be noted that it is not a complete measurement of nutrient in an Aquaponics System, as there are organic nutrients present that an EC meter will not measure. However, over time, the overall measurement is a very useful one.

Conductivity helps you to determine if you are getting the balance between the fish food given or placed in the system, to plant growth.

The range of Electrical Conductivity can be as low as 0.2 and as high as 2.0

In my newest system the reading is 0.5 and is increasing weekly as the system matures and the fish grow.

In another of my Aquaponics Systems that has 126 Sleepy Cod, the EC reading is 1.8. This is a very mature system. The high reading and the maturity of the system indicates to me that I can easily add another grow bed or two.

The same number of fish and feeding regime will easily support more grow beds and produce more vegetables. The EC reading would gradually drift down and find a new level after the grow beds are added and planted out.

Keep in mind that not all the nutrients present in an Aquaponics System will be measured by an EC meter.

As an example of that, in the newer system (Patio Duo) that has an EC reading of 0.5, that system is enjoying good plant growth. Obviously it will continue to improve with time.

You should not attempt to drastically correct low EC readings in your Aquaponics System. Slow and steady is the way. A good variety of fish food is required for the system to be well balanced in nutrients. Make sure your fish are happy and the rest will take care of itself.

As your system matures, if your EC readings are remaining low, you possibly have too many plants or two few fish. Aquaponics is all about balance.

What to feed your fish is the subject of another discussion.

Overall, a good quality EC meter is a valuable tool in maintaining a good Aquaponics system.

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Good to see something else that can give you an idea of how a system is going. I also think DO meters will become more popular in AP and hopefully the price of the testers will drop when more people use them. At the moment AP is becoming the hot topic in commercial hydro systems. With the main problems being the amount of control they have. Tho they seem to be fixating on the fish feed. But the backyard is where I see most of the advances coming from.;)

Barry Peters likes this

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Hi,

I believe that EC meters are useful devices for AP operators. It's important to note, however, that they will not indicate where specific nutrients are missing......and all AP systems are missing some nutrients.....particularly iron, calcium and potassium.

Dufflight.....I agree that most of the development in AP will be around small systems. If, and when, AP does attract the practical attention of the big hydro operators it will probably be the notion of two crops (plants and fish) for the same amount of water that appeals to them initially, rather than the availability of fish nutrients. Nutrient composition in commercial hydro systems is a very precise thing.....much more so than in AP systems.

Gary

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Havent checked my system for a while so went and checked ph 5.2 ec 4.3 oh sh;;t came back and checked meter its spot on test reading ph 4 actual 4.1 ph 7 actual 7.0 my ec has always been over 4

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Potassium and Calcium can be provided the an AP system by using alternately, Potassium bicarbonate (Eco Rose) and Calcium hydroxide (builders lime or hydrated lime) when adjusting pH in your AP system.

It is a natural part of a mature AP system to experience a gradual drift down in pH. The pH can be kept between 6 and 7 pH (close to 7 is better) by adding as an adjuster, alternatively, the two products mentioned above.

This balances the natural tenancy for the AP system to lower pH and adds two of the elements that are missing or short in AP systems in the process.

Iron in the form of chelated Iron should also be added regularly.

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If I may add a little to this Murray.

Pretty important that any calcium is added outside of two weeks of potassium addition and visa versa. Adding the two together means the calcium will bond with the potassium and sink it to the benthos and make it unavailable for plant use.

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are you sure crusty, just thinking in simple terms of anions and cations in solution both potassiumand calcium are positive ions. So they should not from anything.

This does exclude however the possiblity of them forming together with others ions,

NIck

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Hi Nick

One of the basics in pond management. You add NPK or Potassium to a pond to encourage algae growth and you lime the pond to keep the pH stable. You can not do the both together. I am just running from memory but in simple terms (for me anyway) calcium is a potassium inhibitor. I would like to hear differing infos though.

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This is an interesting post just brought to my attention. I'm going to have to disagree with much of what Murray says here. The EC of water is proportional to the amount of Total Dissolved Solids (TDS) in the water. Many people salt their AP systems to 1-3 ppt which would give you a fairly high EC reading. Therefore, someone could be cycling up a new system, end up with high ammonia or nitrites and salt to protect the fish as per standard advice given. Then this newbie reads this post and measures EC. The EC reading could 1.5 - 2.0 dS/m and that person could be given the impression of mature, cycled, balanced system, which is totally bogus.

If you want to measure nutrients in a system, measure nutrients in a system. Most people test for nitrates. You can also get test kits for potassium, iron, and phosphorus. I got a master test kit that does pretty much anything you want to for about $100 CDN. Maturity comes with time.

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Hi,

EC/TDS meter readings are distorted by the addition of salt to an AP system (bearing in mind that it's for the fish rather than the plants anyway)......and, from my limited experience of them, AP systems (even those without salt in them always seem to read much lower than recommended for hydro systems.

Gary

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Bit of an old post resurrection!

 

As part of ongoing management of mineral build up in my system

http://aquaponicsnation.com/forums/topic/8975-build-up-of-minerals-in-ap-water-inc-hardness/page-3?hl=conductivity#entry67359

 

I've started measuring EC.  I've read alot saying that AP system will run happily on lower ECs than recommended for hydro, though what about higher EC's?  One of my systems is running at ~4.5 mS/cm and was up around 6 ms/cm prior to a water change.  It has been salted to around 1.5ppt, though from my calcs using hydro buddy, this should only give around 2.1ms/cm

 

The system has around 200ppm nitrate, around 170ppm Calcium, 7ppm phosphate.  If I assume a K level of 100ppm (I wish!) then hydro buddy gives me a theoretical EC of 3.3ms/cm.   I think the discrepancy is just measuring error (either in EC pen or API test kits).

 

So is there a high limit for EC in AP systems - plants still seem happy.  My source water EC is 0.5 ms/cm, I think I need to either reduce evaporation rates and/or filter source water to lower values if required. 

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Hi Matt,

 

The system has around 200ppm nitrate, around 170ppm Calcium, 7ppm phosphate.

 

So is there a high limit for EC in AP systems - plants still seem happy.

 

There's growing concern from within the medical community about the health risks associated with foods that contain high nitrate levels.....particularly in the diets of infants.

 

So, the question may be more one of "What's the upper limit for nitrates in plants that are intended for human consumption?"  The plant may be "happy" but is it healthy to eat?

Gary

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You could look at common sources of water around you as a benchmark for TDS.

600 ppm is considered good drinking water. Scaling of calcium usually starts at levels of TDS above 500 ppm.

A small creek could be anything from 1000 ppm to 15000 ppm.

 

I think the true value of something like this is when pH and EC are logged very regularly and detailed testing is done at much longer intervals, it is possible to have an educated guess about what is happening just based on where the numbers are heading without having to throw a barrage of tests at the water every week.

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This system has about 4m2 of planted area and about 60g/ day of 32% feed input - Does these figures seem underplanted?  

 

I'd love to have a plant N consumption guide - High nitrates have been a concern to me to Gary from a health point of view and also optimal fruiting plant production.

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I take regular sap nitrate readings from crops, the top growth needs to be stopped suddenly with massively high nitrogen levels available to the roots to get this effect, not something I have seen in an actively growing plant.

Ravnis likes this

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High nitrate readings in system water don't necessarily translate to high nitrate levels in plants... :D

 

That's the kind of nutrient banking theory employed in certain mystical circles... ;)

 

 

Nitrates are just one of the nutrients that are utlised in plant protein formation...

 

If your plant biomass is matched to your feed input... then you probably shouldn't have a high system water nitrate reading anyway...

 

I'd be more concerned about addressing the issue of your system nitrate level.. before worrying about the EC...

Edited by RupertofOZ (see edit history)
Ravnis and bigdaddy like this

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http://www.yara.com.au/crop-nutrition/crops/vegetable-brassica/yield/

 

Yep, its not about how many plants or what growth stage they are at, its looking at the total biomass. Nitrogen and biomass are directly related, anything that restricts growth restricts the uptake of nitrates.

Estimating total growth in a home garden situation is not easy.

 

Farmers and vegie growers think in terms of marketable yield so in the above example the broccoli yield is 13t/ha, the total above ground biomass would be more like 50t/ha

 

if you convert that to Kg (50,000Kg/Ha)

divide by 10,000 (Ha to m2 )

that's 5kg per sq meter

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I agree John, I'd like to focus on getting nitrates down in all my systems - I was toying with EC to see if it would provided a more convenient monitoring method to detect excess build up on minerals compared with API GH & Ca test which I find a PITA to do and discern.  

 

I'm feeding typically at 15g/m2 planted area, with heavy feeders in part of the bed such as toms and corn.  I think this is way lower than UVI rates or even Paul's example in this thread:  

 

http://aquaponicsnation.com/forums/topic/8419-fellow-apn-member-building-the-worlds-biggest-commercial-ap-system/?p=68236 (50g/m2 for lettuce).

 

Though I'm not convinced that it is just a 'matched plant biomass to feed input' issue.  I think my plants are not growing optimally (or even sub optimally in some cases!)  and therefore not consuming nitrates, and this is what I've been trying to get to the bottom of for quite some time ( with close calls of towel throwing in!) , hence my various posts into build up of minerals and zero phosphates

 

http://aquaponicsnation.com/forums/topic/8975-build-up-of-minerals-in-ap-water-inc-hardness/

http://aquaponicsnation.com/forums/topic/9146-0-phosphate/

http://aquaponicsnation.com/forums/topic/8347-most-economical-way-to-test-for-potassium/

http://aquaponicsnation.com/forums/topic/9168-kale-and-corn-deficiency/

 

I'm beginning to suspect a few design factors that contribute:

1) inadequate mineralisation in standard BYAP F&D grow bed system - perhaps there is inadequate oxygenation of water, though fish are not showing signs of low DO

2) excessive evaporation ( I may run my water level too high?)

 

That in part cause

3) Excessive build up of Ca causing lock out of other nutrients - partly due to source water and (2) above

4) Iron deficiency due to no routine Fe supplementation in mature systems / inadequate  mineralisation / high nitrate levels??

5) Low K (perhaps due to over planting of fruiting plants) which then causes all plants to 'stall' - though this in part my be due to (1) and (2)

6) lack of opportunity to supplement K through buffering due to excessive source water use (with its inherent CaCO3 buffering content)

 

So I will try lowering high tide marks and installing solids filtration and MT.  Probably won't go full 'dual loop' at this stage so hopefully this will improve the system mineralisation  enough taken the system closer to a "burginator" approach ( though I'm not exactly sure what that is) ;)  Your systems appear to do very well so there is something to take from that.... have you ever grown lots of fruiting plants in them?  I see that the plants are generally greens with fruiting plants in the wicking beds.

Edited by mattyoga (see edit history)

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I've grown tomatoes, cucumbers, corn, capsicum etc in my (and client) grow beds Matt... including in BYAP kit systems

(My wicking beds are at home on the balcony... not part of my AP system)

 

There are inter-relationships between Calcium, Magnesium and Potassium... and/or phoshporus... (even nitrogen)

 

And a scatter gun approach to supplementing might be doing you more harm than good...

 

If you think you have an issue... address the issue one issue at a time... otherwise you'll never be able to get a grip on what is the cause and effect of your supplementation(s)

 

Measuring your EC is a bit like taking your temperature... It might tell you you're sick.... but it wont tell you why... or how to cure it... ;)

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Edited by RupertofOZ (see edit history)
ande likes this

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Thats good to know John, I understand what you are saying about chasing your supplemented tail!  

 

I've tried the 'leave it it will sort itself out' hippy approach exhorted by some people online (it didn't after a year!), so do you think a MT is the next thing to try (other than flood level adjustment), or filtration to source water?  What type of source water did the systems shown use?  Was it quite hard?

 

 

For the systems shown, how far below the surface to you generally set high tide mark and what would the feed rate per m2 of bed typically be?

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The water sources have been primarily town water, with some rainwater catchment... the systems all running at pH 6.0 - 6.8.... with buffering when required...

 

Never tested hardness levels... (but given pH presumably not "hard")....or added supplements.... other than for pH buffering.... and an occasional dash of Seasol... ;)

Edited by RupertofOZ (see edit history)

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Given your Perth water is generally from limestone aquifers and notoriously "hard" Matty... (with mineral hardness - usually calcium, magnesium & iron)... and usually high pH

 

I really think you should be addressing the hardness and pH issue.. rather than anything else...

 

Then when buffering and top ups are required...  your source water will actually be beneficial..

Edited by RupertofOZ (see edit history)

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I wonder if this is at the core of my issues?  My town water is ph of 8.2, though gets plenty of rainwater catchment in winter, though none for ~6-8 months in 'summer'.  

 

Not convinced its totally at the core as I have issues in winter when I don't top up for 4-6 months, though that may have been due to inexperience in varying Ca/K buffers.

 

edit - posted while you posted John - by addressing hardness/ph do you mean something like RO filtering? (or finding an alternative softer source).  

Edited by mattyoga (see edit history)

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If your pH continues to sit at that level.. then yes you will have continued "lockout" problems...

 

And if you don't address the hardness/pH level of your top up water... then you'll just continue to negate any carbonate hardness reduction through nitrification.. and continue to add/replace your mineral hardness....

 

Why have you been adding Ca/K buffers with a pH so high??... you're just compounding your problems...

Edited by RupertofOZ (see edit history)

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