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How to know if I have enough potassium / magnesium / iron / salt in my system.

My system seemed to be stabilized with PH running around 7 same as my top up water and amonia and nitrites at zero and nitrates just north of zero.

Plants were struggling though until I added some magnesium, potassium and iron so that is cool, however I don't know what are the right amounts, I'm still on the "toss 'er in and see what happens" shoot from the hip measuring plan. Ok well I do measure the potassium chloride one rock / tablet at a time but they vary in size.

I'm getting the hang of knowing some of the deficiencies - does anyone know what the signs are when you go too far with these nutrients?

 

Is there a simple, cheap, easy way to measure these things? I'm a little Dutch and a lot cheap

 

For the record, my system is a hybrid with one IBC growbed using reclaimed clay brick for media and a second IBC DWC with rafts on top and three 55 gallon barrels for fish tanks, one pump in the DWC bed pumps the water to the top barrel and it cascades barrel to barrel to barrel to grow bed to DWC and back up again - the grow bed is constant flood - yep one too many beers when I was thinking that one thru but it's all good

Any thoughts, ideas, brain waves are most appreciated.

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Darn Vlad, you caught me skimming and not reading.  Granted I was multitasking albeit not well.  Found the pdf, thanks.  Still trying to get you that book btw.  I was just talking about the absurdity of the cost of postage to your house the other day.

http://www.scribd.com/doc/116298550/Hydroponics-A-Practical-Guide 

Vlad, this is fascinating.  I always like find a good reference just skimmming through this I found some contradictions to some of the stuff I have learned by listening.  It will be interesting to go find the papers they site in this book.

Since chemistry is not my strongest suit, it mentions chelate iron inhibits Zn uptake(pg 60).  While the solution for this inhibition is to simply increase the zinc concentration it seems as if that is the easest fix, he does mention non chleated iron does not have this effect.  I am unaware of a non chleated product that is available in solution without an anaerobic "digester".

No sweat Matthew. We're all guilty of skimming sometimes. Yes, J. Benton Jones Junior is one of my favorite "tomato" guys. I own a copy of that book and cite it incessantly at times. Many of the papers and people cited therein are real good too. Check out A.P Popadopoulos work on cucumbers he did while at the Harrow Research Station in Canada...Good stuff. I've posted links to his work here before...But since you brought up the moral/legality issues of doing that type of stuff, I've generally quit linking resources here and just drop names...if people actually care, they can then dig up the research/books themselves without the possible headaches for Sylvia...

As to non-chelated iron sources...Sure they exist. Hydroponic folks had to have used something for iron before chelates existed, right? MaxiCrop + Iron still uses one such substance...Iron sulfate, Iron citrate, Iron Chloride and others were used before (and sometimes still are) instead of Fe-chelates. It just takes a lot more of this 'type' of iron in solution to be useful than with Fe's chelated counterpart.

As far as Zn, I think you may have gotten that a bit backwards Matthew...Excessive levels of Zn are known to somewhat interfere with Fe uptake, while the reverse has not been proven yet, and is still a matter of dispute in the scientific community.... Many things surrounding some of Fe's different functions in plant biology are still not understood fully or real well by humans yet. Some of the chelating agents used just complicate issues even further...But, yeah you can use other sources of Iron, but then things like pH and things like phosphate levels really need to be kept even more controlled. In an AP system the pH needs of the bacteria interfere with this, while the fish, and the 'high' level of phosphates that their fish poop contains, interfere on that side of things...I still think an RSG filter and an organic chelating agent (like Oak tannins) would work in an AP/bioponics (particularly if you have a handle on your pH), but honestly, I've not had the time for that little project. I've laid out the theoretical blueprints elsewhere here on the forum, and was hoping that someone else would run with it. (Eric Warwick perhaps...I think it would make a great science project for school, while at the same time being something 'new' and potentially useful to other aquapons who wish to avoid industrial Fe-chelates for whatever reasons (sustainability, self reliance, health fears surrounding chelates...whatever).

Yes, many things are absurd here. Most of that has to do with the business arrangements between with your "managers" and mine...Meaning our governments and the tycoons who run them. Things are different though, if we were to interact more personably, as private individuals and circumvent business arrangements between governments. i.e...if you were to send me that book as a friend, from your own hand, and from your own address, shipping would be 10 to 15 times cheaper...and if you stated the value of said book on the little form from you fill out at your local post office as being $5 to $10, that would go a looong way in lessening the customs duties, taxes etc... that I would need to pay on my end. To quote Monty Python ..."wink wink, nudge nudge...".

Since you are obviously very knowledgeable about fish, and had recommended Nogas book, my wily self went about securing a PDF copy...But to put it bluntly, my PDF copy sucks ass. Not because of Noga or the content, but the person who scanned the PDF did so in a manner where all the text is fuzzy and 'blocky'...Which makes it very difficult to read (actually it gives me a headache when I try...and the color photographs which I consider an invaluable supplement to the text, are unfortunately totally useless in such a crappily scanned PDF copy such as the one I posses 

Hey gent's just wanted to check in with a short update - I've been able to add the Fe and KCL so far, still working on the Mg slowly via epsom salts and there has been a significant up-tick how the plants look and are definitely starting to takeoff.

So thanks for all the help on this most appreciated as always. Also, thanks for the great link for the hydro book - I don't know if it was meant to be read cover to cover but seems that what I'm doing with it. I'll have to get a hard copy it'll be a great reference.

Sorry about the delayed response, this working for a living thing is getting in the way of my aquaponics habit!

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