DTPA or EDTA? - The Planted Tank Forum
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post #1 of 7 (permalink) Old 01-18-2013, 09:42 PM Thread Starter
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Plant fertilizers are available as liquid or substrate fertilizers. Both should only contain the micro nutrients. Liquid fertilizers have to be dosed more frequently; substrate fertilizers will last longer. Since there are no obvious differences in efficiency, it is up to the aquarists' preference which to use.
Next to the micro nutrients, fertilizers contain chelates. The chelate is an organic molecule which binds metal ions thus protecting them from early precipitation. The preferred type is abbreviated DTPA because of its stability up to a pH level of 7.5
Unfortunately some fertilizers contain the chelate EDTA, which is much cheaper. However chelate EDTA is only stable at a pH up to 6.0 and therefore mostly useless in aquariums.

What do you think?

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post #2 of 7 (permalink) Old 01-18-2013, 10:45 PM
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What type of aquarium are you running? i.e. south american, african, etc. My Quantitative Chemical Analysis textbook shows that EDTA is capable of chelating metal ions at various pHs, depending on the major species of EDTA present (metal-EDTA complexes become less stable at lower pH ranges.)

Also, you can use any pH value to select which metal ions you want to be chelated by the EDTA and which ones will not be chelated. (example from my book: if a solution containing both Fe3+ and Ca2+ is titrated at pH 4, the Fe3+ is titrated (chelated by the EDTA) without any interference from Ca2+)
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post #3 of 7 (permalink) Old 01-19-2013, 06:55 PM Thread Starter
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800 L planted ph-6.5 light=1w/l tds=135
can please guide me how to add a picture from my iphone?
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post #4 of 7 (permalink) Old 01-19-2013, 11:02 PM
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When you go to type in the "Quick Reply" box below my post, you can click on "Go Advanced" and it will bring you to another page. On this page, about halfway down, there is a button that says "Manage Attachments." From there, you can upload pictures straight from your computer.
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post #5 of 7 (permalink) Old 01-19-2013, 11:17 PM
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You have to also include water hardness as ngrubich eluded to with his Ca+ example.

You won't be able to see a difference between DTPA and EDTA if you're dosing EI. Iron is a trace element so you don't need a lot and the difference(if there is one) between DTPA/EDTA will be masked by a lot of other variables that have greater effects on the plants (light, CO2, other traces, etc.).

Last edited by UDGags; 01-19-2013 at 11:17 PM. Reason: updated spelling
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post #6 of 7 (permalink) Old 01-20-2013, 12:16 AM
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Above the pH levels you listed, they do start breaking down at a rate dependent on pH.

For long-term storage in a bottle, Fe EDTA is therefore best kept at 6.0 pH or below.

Dosing every day or every other day, the breakdown rate for Fe EDTA is insignificant at 6.5 pH. Probably for weekly dosing too.

At 8.2 pH is another story - I had to do daily dosing of Fe EDTA at 3X recommended amount to prevent iron deficiency. Switching to DTPA helped greatly here.
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post #7 of 7 (permalink) Old 01-20-2013, 06:41 PM
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ETDA and weaker chelators or ligands do NOT break down instantaneously.
So if you dose daily etc, or if you used say DTPA 2-3x a week, the results should be similar.

I use ETDA, Fe Gluconate and DTPA all in one.
I buy Fe Gluconate and DTPA and add to Plantex CMS+B.

Cheap and will last about 5-10 years for maybe 50$ worth.

Tom Barr
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