Long ago I found i needed more iron for things to look good, and upon some guidance about Ph and Seachem iron, I switched to 11% DTPA mixed.

I am adding iron daily at a rate of about .4ppm (specifically as an example in my 40G I add 5ml of a mix of 54g 11% DTPA FE and 500ml of water). My tanks run about 7.6-7.8 ph, dkh=4-5, dgh=7 @ 78F and with about 9 hours of low to almost medium light.

By the next day it is almost all gone. I am testing with the Seachem Iron test, waiting the 45 minutes suggested, and I get a trace in the low-range test (I'd estimate about 0.01 - 0.02 at most). I have tested the test with the included iron reference sample and it worked fine. If I test immediately after dosing I get approximately the expected value (maybe .2-.3 instead of .4, but a substantially higher reading in the right ballpark).

The tanks are low tech (though i do use Excel), and moderately planted. I've included a recent photo of each to give some feel for density since "moderately" is subjective.

How should iron behave? Does such rapid dissipation indicate that I am not dosing enough? Can this density of plants actually absorb that much, so quickly? Or is it precipitating out or otherwise disappearing for non-nutrient reasons?

I am trying to dose for a more steady state environment with infrequent water changes (say every 30 days), so I do not want to over-do it, at least substantially so.

Should I just keep increasing until after 24 hours I still have, say, 0.1ppm or so?





PS. I do use Osmecote+ root tabs in addition.

PPS. For reference, as I read it, the PPS-Pro recommendations are for about one quarter this much iron daily.

Perhaps someone will post a list as I can't find it right now.
But the EI dosing recommendation is .5 ppm on your type of Fe.
I have two 10g tanks and the one/w Rotala in it needs more than .5 or I get iron
deficiency symptoms. With 1/16 tsp of CSM+B I get .46 of Fe and that still gives me the symptoms if I don't add a 1/64 tsp of the Fe 10% that I use with it.
I don't use injected CO2 so I only do one dose of the EI per week, but do two doses of the CSM+B and the Fe. Because I was told that Micros only last a short time and that it would be best if I did at least two doses of it.
I don't know that any of this will be helpful. I realize that I did not directly answer either of your questions. But thought it may help in some way.

Well, that's a good example of what concerns me. The EI Daily recommendation appears to call for only half the iron I am already dosing.

PPS-Pro is about half that.

So I am already way higher than these regimes call for, yet after 24 hours it is virtually all gone.

That's why I am asking about how it should behave -- maybe I should not expect to see any on a test in 24 hours?

Incidentally, I do not have any obvious iron deficiencies, however, I do have more nitrates than I think I should, which leads me to wonder if I am nutrient limited somewhere causing the plants not to take up as much nitrates as they should. I did have some potassium deficiencies (at least I think they were) and doing some math realized that was likely, and have been adding more.

I also had GSA problems and started adding more and more phosphate until I got that up to a reasonable number (around 1.5-2) and the GSA is better.

But Iron is at least in theory just a micro, but I seem to be shoveling it in pretty hard, and want to know if I'm off base in how I am looking/testing?

No one else?

I've been trying to read about the behavior of iron in water. A good discussion is here, though the concluding paragraph reads as follows:

After reading the whole article I understand more of the possibilities but I do not quite know what to do about it. Some paths seem to leave iron available, some do not, and the vague comment about iron toxicity is a bit of a concern.

My main question, I think is simple -- if I use the Seachem test, and it shows negligable iron after 24 hours -- is there any danger of upping the dose until I start seeing some significant amount at 24 hours, say 0.1ppm. Is there any way to build up toxic levels (or other harm beyond cost) of trusting the test at the 24 hour point?

Any good water chemists out there?

After reading the article you posted, there does exist a risk of overdosing iron on a repeated basis (even though measurement 24 hours later may lead you to believe your iron levels are low). There are many competing processes which will take soluble iron out of the water column, which act relatively quickly, and unsurprisingly 24 hours later you will not detect much. Some of the iron though will be absorbed by plants (and fish?) and without any restraint will lead to toxic levels.
This leaves the daunting task of measuring the effectiveness of your iron dosing (because the water column is not right place to measure it).
Short of taking a leaf sample to be lab analyzed, what do you do?
I agree with Raymond that the plant should be the indicator, and eventually you will come to understand the iron requirements of your plants. Perhaps the discussion should be how to detect when your plant shows an iron deficiency (zapins - where are you...).
The article suggests that a lower pH water helps make iron available to plants (a tannic chelation can be used by plants), and recommends using tannic acids to achieve this rather than an approach which requires dosing iron at higher levels (but of course this is not practical for many).
Until a good chemist addresses this issue, and since you said you do not see any signs of iron deficiency, it seems to me that you should lower your iron dosing for now.

with any new plant/garden I give it a decent base and then feed minimally, then address any deficiencies as they appear.. this is how I get a good idea of what they really need and dont need and work my way up.. chemicals are expensive and can lead to bad things if not used sparingly.

Unless a plant is really sensitive it can take quite a bit more than you should be giving it to show Toxicity levels.. and I find diagnosing this to be much harder because resistance is pretty hearty in most species.. Riding the minimal nutrients a plant needs to survive is healthier and safer than opposite coin of finding the maximum levels you can obtain.

Its a minimalistic approach, but under fertilizing (Deficient) is much easier to trigger and quicker to take care of than over doing it (Toxic) and so yes imho if you havent seen any iron decencies you should cut back dramatically and see if that remains to be true..

Well i'm not a chemist but there should be some simple tests you can do to at least narrow down the problem.

You say that immediately after dosing you get good iron levels from your tests. Have you tried taking a water sample and letting it sit outside of the tank for 24 hours and then retesting? If it is reacting with something dissolved in the water then the sample should show the same symptoms as the tank.

Also it could be getting adsorbed by the substrate in some manner. You can repeat the above test but this time add in some substrate to the test vial and see if the results change.

A substrate with a high CEC should adsorb nutrients out of the water, that is the whole point of it, so it could be your substrate. Though I don't know how well it absorbs minerals like iron compared to other things.

aja31, that's a good idea. I can do a separate container test easily. My substrate is black diamond blasting sand, so in terms of the substrate itself I don't think it is an issue, but it is pretty deep and now has lots of biologic activity (plants + poop + snails) so who knows what happens there.

You add iron in the morning and by the next day it's almost all gone. Depending on the amount of plants and size will determine how much is being absorb by plants. As the plants get larger they will need more iron. My friends small tanks one heavily planted and one not so much absorbs less. Do you find when you cut back the iron doesn't deplete as fast?

OK, now I'm confused. aja31 had a good idea, and it is giving me a clue, but I'm not quite sure what to make of the clue.

I added the iron to my smaller tank, and let it circulate for about 15 minutes, thinking that would mix but not absorb. I measured it with the test and got a bare trace -- maybe 0.01 or so.

So I tried the reference sample again. I don't know if something changed, or I multiplied instead of divided months ago when I tested it, but this time I mixed for a 0.8ppm and measured 0.1ppm. So the test looks really low.

I then tried making my own reference sample, took 10,000ppm and diluted 5ml in 495ml, then mixed that and did it again as 5ml in 500ml... should be 1ppm, right? Ran the test (waited the full 45 minutes) and got about 0.05. Very low.

For anyone with the Seachem test -- what I am doing is using the low range curvettes. I am using 1 scoop of reagent, filling to 1cm of the top, mix, and waiting 45 minutes then measuring by looking down into the it (though the longest distance), and dividing that reading by 4.

Divide -- right? If I was multiplying I would be much closer to what I expect in both cases.

So the test looks wrong? Gone bad over time (bought it about 9 months ago). Seachem doesn't put an expiration date on it.

I guess I'll post a note to their forum, see if they have a comment. I would hope a test doesn't go bad that fast (I got it from Amazon, which I would hope has quick moving stock).

are those congo tetras? They are gorgeous!!

Yes, and thanks -- they are getting huge, and nicely orange. But seriously huge, I worry my wife may get hungry for a fillet one day and grab one.

lol! I am getting some next time I see them. Your pics convinced me

We're kind of off subject but since you asked and I was in my photo library at the time doing other work, here's a real photo of one:

beautiful colors! Usually they are duller at the store. I've been wanting some and now I'll have some, lol! Might take my emperors back.