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PostPosted: Jul 2nd, '16, 17:23 
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Thanks for the feedback

Update for others who may be experiencing the same issues re Ph and balancing nutrient requirements

Purchased:
    Kelp extract solution
    K Hydroxide flakes (25kg lol)
    Ca Chealte
    Mg (Epsom Salt)

PH Management
Add K Hydroxide (50g) when Ph at 6- 6.2
Ph climbs to 6.4-6.5 over night (6000l system)

TDS has dropped to 420 from 1/3 water change topped up with bore.
Foliar feeding weekly with Kelp sol 30ml/ 5L + Ca 1gm/L
Top up Fe and Mg monthly directly into the ST

I have worked out the amt of Fe to add but not mg at this stage, Anyone know dosing requirements for Magnesium?


Funny thing discovered today;
Pre this new management plan nitrates have always been off the scale
I assume the plants were not consuming due to the above missing requirements.
Feeding the perch took a back seat whilst I tinkered with the above.

Today I paused to think again about the plants. Its been a month with the new management plan, I could see they were perky again, alive and ready to grow but not doing so.
I decided to checked Nitrates..... DOH! very low
Aquaponics 101 :oops:
At least this is a quick and easy fix.
They must have though it was Christmas today.


Happy days...


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PostPosted: Jul 2nd, '16, 20:10 
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I always thought the epsom had to be applied by foliar feeding, maybe someone with experience with this can comment as I haven't tried/needed to before sorry.

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PostPosted: Jul 2nd, '16, 23:46 
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Hi Charlie

Maybe I dont need to apply magnesium at all
I am fairly sure Nate was the source of this idea that It needed to be added to AP systems.
I may have heard incorrectly. He may have been discussing Ca K and Mg and how they compete re uptake, I may have taken it as needing to be included as an additional requirement.

I will give it a go without and observe..

Thanks


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PostPosted: Jul 3rd, '16, 01:04 
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Pretty sure it doesn't matter Charlie. I know it doesn't take much either way. I got the impression that Nate was suggesting it only if the plants were showing signs of a deficiency even though he suggested regular dosing for those systems that weren't getting enough.


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PostPosted: Nov 27th, '16, 10:01 
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Update

It's now been 1 season. It turns out that when my plants took off, they used up the chemicals quickly. I went on a 20-day vacation in June and when I refurned, my pH was nearly 5. Everything was fine but ph not as steady as I had predicted. I added a teasoopoon of KOH and CaOH 1-2 times per day to bring pH back up with some mkp with each add. It took a couple weeks of this to bring pH back up, because I wanted to do it gradually.

Also, I think I may not have enough egg shells to keep up with my systems needs so next year, I'll try a bigger bag of coarse oyster shells.

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PostPosted: Nov 27th, '16, 18:07 
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HI Scott

I think the plan looks sound. I use basically the same but I add Iron on top of the above.
Even though I too use bore to top up I notice i drops to below .05 ppm if I dont.I add 70 to 100 mgs every few weeks of this form: FeDTPA My system is also 6000l.


Im adding KOH when Ph drops to 5.8 keeping system at 6 to 6.2 is being helped by the addition of 2 massive Limestone rocks. Set and forget. They work the same way as the egg shells, increase dissolved ca carbonate to push Ph higher. Adding KOH is stiell required when ph low or every other week for plant use even if ph ok as the system wants to return to acidity anyway

I am not sure about the amount of Ca Carbonate and its effect on the uptake of other minerals for the plants. Im still experimenting with this.
Enjoy the tinkering :)

J


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PostPosted: Nov 28th, '16, 00:21 
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Instead of guessing - get yourself a pool colorimeter or some equivalent( iorodeo.com) - they cost around $150-200. Then you can measure calcium and calculate your magnesium amounts. I personally use the iorodeo one and I have been working with them to add more tests for aquaponics. You typically want your K and Calcium in the 50-100 ppm range. Mg should be in a 1:3-1:4 ratio to Ca (calcium being more than Mg). You can add epsom salts to increase Mg but note that you are also adding a decent amount of sulfates.

Hope that helps!

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PostPosted: Nov 28th, '16, 07:13 
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ebeuerle wrote:
Instead of guessing - get yourself a pool colorimeter or some equivalent( iorodeo.com) - they cost around $150-200. Then you can measure calcium and calculate your magnesium amounts. I personally use the iorodeo one and I have been working with them to add more tests for aquaponics. You typically want your K and Calcium in the 50-100 ppm range. Mg should be in a 1:3-1:4 ratio to Ca (calcium being more than Mg). You can add epsom salts to increase Mg but note that you are also adding a decent amount of sulfates.

Hope that helps!


How about some info for those of us that can't spend big bucks for test equipment? And don't have a through understanding of chemistry? I just have an API test kit and ph runs around 7.2 to 7.8, water is clear, plants are doing great and the fish are over joyed! It seems to me that as long as everything is working fine why keep messing with it. Over a year now with no lost of fish or dying plants. Just curious as to why y'all do what you do. Maybe you have commercial aquaponics with expensive equipment?

Just asking.


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PostPosted: Nov 28th, '16, 09:40 
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There are a lot of variables and components to an aquaponic system and the more you understand, the better you can make your system perform and grow healthy veggies. I am glad your system works well for you but every location and every system is different and thus by applying some science, it can allow you to get the most from your system.

I don't know what kind of plants you grow, but often people run into problems when they try to raise fruiting plants because of a lack of specific nutrients from the fish waste alone. By testing the water, you can determine what needs to be added to fix the visible deficiencies and often the unseen ones as well.

Since we have to provide most of the inputs to our systems, we are responsible for making sure we add the right amounts to ultimately grow healthy food for ourselves and our families. I prefer to take some of the guessing out of it but I understand some prefer to not "mess" with it.

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PostPosted: Jan 22nd, '17, 11:58 
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scott_dc wrote:
I've seen lots of bunk and discussions from people that obviously don't know much about water chemistry (but claim to). While I don't know much about fish or plants except what I've read here, I have experience in inorganic water chemistry so thought I'd contribute some knowledge.

This is what I do and why. Feel free to do something different or disagree.

I use rainwater. I think the same method would work with hard water that was treated with hydrochloric acid (muriatic) to neutralize pH but I haven't done this personally.

Here goes:

1) CABONATES DO NOT BUFFER pH IN THE RANGE OF INTEREST TO AQUAPONICS. If your pH is stuck above 8.2 or so, then carbonates are to blame. If your pH is below that (say, 7), any carbonates will form an equilibrium between bicarbonate and dissolved carbon dioxide. The carbon dioxide will be in equilibrium with the atmosphere. Any excess carbonate/bicarbonate will form carbon dioxide and be released to the atmosphere. Some of these reactions can be slow (days), which can be good or bad, but this is not buffering.

2) The only effective buffer I have seen that is good for plants and fish is phosphate. Some organics might work but they or their breakdown products would probably be bad for fish or plants. Phosphate is a very effective buffer right in the pH range ideal for aquaponics. I try to maintain about 50-100 ppm phosphate in my system by occasionally dosing with mono-potassium phosphate (mkp). It doesn't take much and the phosphate doesn't get used very quickly. I measure it with the API phosphate kit (works to 10ppm so I have to dilute to measure). I've seen lots of posts that say to avoid too much phosphate because of algae blooms. However, I keep my fish tank shaded and have had no problems with algae. I can understand why phosphate is bad for aquariums and ponds (exposed to light) but I want my water to be conducive to good plant growth--that's the whole point.

3) The nitrification process decrease pH over time. This requires periodic adjustment to maintain pH in a good range. I don't think there's any debate on this point. Part of me thinks that plant roots put out chemicals that decrease pH too. That's how they get nutrients like Fe from the soil (or so I've read).

4) I previously added potassium hydroxide and calcium hydroxide to keep pH up. I did this because of various posts/threads that said carbonates are bad because they buffer pH too high. The phosphate noticeably decreased the frequency of adjustments and allowed me to add more each time without dramatic pH swings. This is the point of a why I added the buffer (phosphate). However, pH did still swing up with each addition and drift down over time.

5) Realizing the chemistry noted in paragraph 1), above, I put in a mesh bag of egg shells, which are calcium carbonate. If completely dissolved, they would increase pH too much. However, they only slowly dissolve. Higher pH makes them dissolve more slowly and lower pH more quickly. This is just what I want. I keep the bag in the water. If the pH starts to creep too high, I take the bag out. Too low, put the bag in. Other forms of calcium or magnesium carbonate would work (limestones, oyster shell, probably any growbed media that fails the vinegar test). Note, i don't crush the shells because I want them to dissolve slowly.

6) With the combination of the phosphates buffering the pH (paragraph (2)), and the egg shells slowly dissolving, my Ph remains rock steady for weeks on end. THe bag stays in for several weeks, then come out for a week or so. No pH swings, pH always in a good place.

7) I dose with maxicrop and potassium nitrate as needed to keep K in line with Ca. Some have suggested that I may have a Mg issue so a dolomitic lime might be a good option instead of the egg shells. I also occasionally dose with very small amount of epsom salt but I don't like to because I can't measure Mg or sulfate and I don't want it to build up.


please let us know how you control your chemistry and/or how I can make mine better.




Thanks for bringing this (MKP buffer) approach to my attention Scott.

I have had my system going since May in SE Queensland, Australia...

everything was going swimmingly well, until a sudden ammonia spike a couple weeks ago. Long story (which I will need to write up on a page describing my system), but I believe that it was a result of the combination of using relatively low pH (4.9) rainwater and hitting a tipping point with the fish effluent/ammonia/nitrification.

Anyway, I've been struggling trying to maintain a reasonable pH in the AP system, it tends to 5.0
I have been adding hydrated lime and potassium bicarb, alternatively 3 to 1 respectively. Great, sends the pH up to 6.5, but by the next morning it is 5.0 again. Cant be good for the fish. Fish seem happy enough but, still I'd prefer more stability for them and for me.

I have added about 3 kilograms of shell grit into the FT and sump. So that should help reduce the pH decline... however I didnt expect to, or want to add chemicals each day to maintain a decent pH.

I am suprised that there has not been more discussion of your approach as it is a bit different to "consensus" according to many AP experts teachings found on the web, and in workshop I attended.

Anyway, cheers and hope your system is going to have a great growing season this year.


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PostPosted: Jan 23rd, '17, 05:09 
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Just note that Scott_dc is using calcium carbonates in addition to the phosphate to buffer the system. Adding carbonates in the right amount is key to keeping pH stable in your system. You can use the API KH test (alkalinity) to monitor the carbonate buffer and add as you see it drop. Hydrated lime is primarily calcium hydroxide and does not provide any buffering - it will raise the pH though. Your addition of potassium bicarb is the only carbonate source and based on your 3:1 ratio, you are probably not adding enough carbonates to keep the pH stable (check via alkalinity test).

Also, too much phosphate can cause toxicity in the plants so be careful solely relying on a phosphate buffer and make sure to take measurements.

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PostPosted: Jan 23rd, '17, 05:19 
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ebeuerle wrote:
Just note that Scott_dc is using calcium carbonates in addition to the phosphate to buffer the system. Adding carbonates in the right amount is key to keeping pH stable in your system. You can use the API KH test (alkalinity) to monitor the carbonate buffer and add as you see it drop. Hydrated lime is primarily calcium hydroxide and does not provide any buffering - it will raise the pH though. Your addition of potassium bicarb is the only carbonate source and based on your 3:1 ratio, you are probably not adding enough carbonates to keep the pH stable (check via alkalinity test).

Also, too much phosphate can cause toxicity in the plants so be careful solely relying on a phosphate buffer and make sure to take measurements.


Thanks Eddie. I've added shell grit only a couple days ago, so hoping that will start to assist with reducing the rate of pH decline...

In fact this morning the pH was 5.2, previously it had dropped back to 5.0 by morning.

My KH is below detection (API test kit). So, yep, definitely not enough carbonates in the system. It feels as though all of the carbonate from the potassium bicarb is being quickly consumed within the system each day. Putting me back to square one.

The other thing I have to factor in is occasional use of tapwater, having KH of 70ppm, pH 8 and contains chloramines :shock:

I rely on rainwater as much as possible, but sometimes run out when there is a period of no/little rainfall.

Will keep testing. Thanks for reply.


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PostPosted: Jan 23rd, '17, 06:11 
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Rainwater tends to have very little carbonates so you will need to add a decent amount to your system if you aren't using your tap water. Just be aware that at the low level of pH you are at(5.2), your nitrification is basically completely stopped and you may see increases in ammonia/nitrites which could harm or kill your fish. You need to bring your pH up slowly but at a minimum of 6.0 and maintain it there.

You may want to start using the tap water however at this point it might be dangerous since the bacteria will break down the chrloramines into ammonia and you are already at risk of ammonia from the lack of any nitrification.

Shell grit can work but it will take time to dissolve - if you can find some powdered shells or calcium carbonate that might help as well.

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PostPosted: Jan 24th, '17, 11:24 
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To be clear on terminology:

In the sense of the word as used in chemistry, carbonates do not "buffer" the pH in the range of interest to aquaponics. The effective buffering range for carbonates is just above a pH of 8, which is where you'll see lots of people's pH get stuck if they're using ground water. It's stuck because the carbonates buffer pH and make any change (increase or decrease) require lots of chemicals.

In the pH range of interest to most aquaponists (say, pH of 7), carbonates react to form excess carbon dioxide in solution, which takes time to equilibrate with the atmosphere (hours to days). Coincidentally, calcium carbonate (shell grit, limestone, egg shells) has low solubility and dissolves slowly at pH of around 7. These slow processes are beneficial because they help to stabilize pH but these processes are different than a "buffer" in the strictest sense of the word. The difference becomes most important when you're trying to do something like adjust the pH of hard water. You need to recognize there will be a sudden drop below 8 after the carbonates are 'consumed' and you need to recognize that the slow equilibration process requires you to let the water sit a day after the adjustment--as carbon dioxide leaves solution, there will be less carbonic acid formed and pH will increase again.

Phosphates do buffer pH around 7.0. However, as I noted in an earlier post, they are consumed by plants so maintaining a specific level might be difficult. However, keeping some low level (say less than 100 ppm) does help stabilize pH and is not toxic to plants or fish.

If you need to adjust to pH upward and shell grit isn't dissolving fast enough, I would recommend small amounts of potassium bicarbonate in addition to something like shell grit.

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PostPosted: Jan 24th, '17, 11:38 
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scott_dc wrote:

If you need to adjust to pH upward and shell grit isn't dissolving fast enough, I would recommend small amounts of potassium bicarbonate in addition to something like shell grit.


Hi Scott,

yes I am having some success over the last few days with potassium bicarbonate plus shell grit. I have gone a step further and pulverised some shell grit in mortar and pestle.

My system was drifting back to 5.0pH every morning. over the last few days it is 5.1, 5.2, 5.4 this morning.

I havent pursued the MKP further, yet. Will see how stable I can get my pH with shell grit and potassium bicarb.

Fun, isn't it? :think:


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