Seperating macros from micros

[Matan Golan]

Hi everyone,
I was wondering if there was a special reason for the separation of the macro elements from the traces while dosing. Is there some kind of chemical reaction that occurs if they are mixed? Are they less available for the plants this way?

It seems all commercial companies supply them separately and most dosing regimes, including EI, recommend dosing them on different days.

I can understand that it's important for people wanting to control concentrations of specific elements in the water, but for the avarage hobbyist that doses without measuring concentrations in the water it really does'nt matter...

Thanks,

Matan

 

[VaughnH]

The only major problem with traces and macros is that iron and phosphates will combine to make a precipitate. If you tried to premix all of the ferts in a bottle of water for easy dosing, most of the iron would be at the bottom of the bottle as a solid powder. But, for dosing separate ferts in the aquarium you can dose them one right after another, and at worst the iron will end up on the substrate where it will only be available to the plants through the roots. If you dose the traces first, then wait a couple of hours and dose the macros, there should be no problem at all.

 

[Matan Golan]

That makes sense.
Thanks a lot.
Matan.

 

[Neil Frank]

I like to keep dosing simple, so I would like to revisit this issue to make life easier. Do PO4 and Fe really have to be dosed on separate days? No. Do they have to be dosed hours apart, I also say NO!

I find it very difficult to remember what I dosed the previous day. It is much easier for me to do both and be done with it! So, is the need to add Fe and PO4 on separate days to avoid precipitates a MYTH?

In concentrated solution, mixing iron and PO4 is a bad idea. FePO4 precipitate can/will form. So keep your solutions separate. However, this should not be a concern when mixed in the aquarium where levels are MUCH lower.

Keep in mind that when traces are added to the aquarium water, the PO4 level is not zero. Think about folks that have PO4 in the tap water. Similarly, i assume that when PO4 is added, the Fe is also not zero!

With the dosing commonly discussed in this forum, the water column PO4 levels may always be near the target levels 0.5-2.0 ppm. Yes, there would be reductions from the intial levels with PO4 and Fe uptake, but concentrations are still there day(s) after dosing.

My recommendation: After a Fe/trace or PO4 dose has a chance to mix and dilute in the aquarium, the other one can be added. I dont think it should even matter which is added first.
(One cavaet i must add: I currently use TPN with DTPA and HEEDTA chelators. However, i cant see why this would matter with Fe-EDTA unless there is none in the water column after 24hours. BTW, Seachem also recommends dosing P and FeGluconate on the same day. See Seachem Dosing Chart)

Now, is there a different reason and possible advantage to spreading out the dosing among days: Yes -- to keep the concentrations more uniform and consistent. Thus, continuous or daily dosing would be better than everyother day which may be better than weekly. This is likely more important with lower dosing rates to achieve low target concentration levels. The situation may be different in mixed plant communities where some nutrient hog like Echinodorus can suck up all the nutrients and starve some smaller stem plant. Then low concentration dosing would be a problem and higher levels would be better. I can also imagine that more consistent chemistry can be important for some plants like Cryptocoryne, but then there is the issue with the 50% water change.

 

[Tom Barr]

My typical tank water sits about 3-6ppm of PO4 on any given day.

I add plenty of traces, Fe is the one to worry about.
Since I can alter the chelators, I also have soft low KH tap water, bout little over 1 degree, I use a mix of chelators, Fe Gluconate(weakest but mos available to plants), ETDA(middle range, still fairly weak), and DTPA which last a few days but is the strongest and least available to plants.

These "availabilities" do not play a huge role I'd argue as Fe is only a tiny fraction of the energy used for nutrient uptake, whereas the largest would be for light gathering and CO2 uptake(several orders of magnitude difference here) or even Nitrogen etc.
It's not a huge energy demand.

So overall, while ETDA is cheap, DTPA might be better, ETDA is good for daily dosing and Fe gluconate is as well.
I think daily dosing with Traces is more useful than most other nutrients. At least from what I've seen, even though I may be a little skeptical about that even and with caveats.

Regards,
Tom Barr

 

[Tom Barr]

I like to keep dosing simple, so I would like to revisit this issue to make life easier.
Now, is there a different reason and possible advantage to spreading out the dosing among days: Yes -- to keep the concentrations more uniform and consistent. Thus, continuous or daily dosing would be better than everyother day which may be better than weekly. This is likely more important with lower dosing rates to achieve low target concentration levels. The situation may be different in mixed plant communities where some nutrient hog like Echinodorus can suck up all the nutrients and starve some smaller stem plant. Then low concentration dosing would be a problem and higher levels would be better. I can also imagine that more consistent chemistry can be important for some plants like Cryptocoryne, but then there is the issue with the 50% water change.

If you like this line of reason, then using a rich sediment is right in line, soils provide a lot of Fe, often in reduced form. So lower target concentration can be done much easier and the sediment provides a back up.
ADA suggest extactly that.

It's also easier.

Still, as far as risk and issues, I think if "easier" is the goal, then higher dosing is less risky.
It provides a workign range that is a lot easier to hit and target than some low level concentration.

Why drive on a narrow road when you can hog the highway?
Which is easier and safer?

Same deal here.

Below is a typical uptake vs growth rate/yield graph.
Concentration can be in the => media/water/sediment etc as they used here or in the plant itself. The graph shape and ranges will be the same overall still.
Most monitoring or nutrients and growth studies do both, one to confirm what is the media, and the dry weight concentration to see what the plant actually is taking up repective of any other factors, eg, there might be high NaCL blocking uptake, but plenty of NO3 etc.....

D is obviously the easiest range to hit, not B or even C.


Regards,
Tom Barr

 

[Philosophos]

I find it very difficult to remember what I dosed the previous day. It is much easier for me to do both and be done with it! So, is the need to add Fe and PO4 on separate days to avoid precipitates a MYTH?

I've wondered the same. I find the reaction between CaCl2 and MgSO4 to be even more violent, but dosed an hour apart I'm not seeing precipitates there either.

I alternate days more because I don't always want to hang around after morning dosing, waiting for things to get into solution. I use one graduated cylinder and check the color of the crystallized residue from the previous day to remember what I dosed, then rinse the thing out. Writing a weekly schedule is futile for some of us.

Perhaps the interaction is worsened for those who dry dose. Many just dump straight in without premix, or don't get things into full solution, or skip steps and stick both in at the same time. I agree with Tom on keeping a wider path, especially when addressing a wide audience. Sometimes it's easier to just presume you're teaching, "the slow kid who rides the short bus" for the sake of everyone's tank and your own sanity.

 

[Tom Barr]

That's the trade off for being general, it must be a wide path to factor all the variation folks have.
Too narrow, specific, then a narrower path etc.

There's a simple thing for folks: practical management.

Some might be abkle to manage a tank at say the "C range" very well.
But is this a requirement?

I do not think so.

It also does not imply that a person who can have a nice tank at the C range is "more advanced", or"Better" than someone who opts for the D wider range.
Both ranges yield the same growth and results.

An adavnced person might reason that D is a wider target, thus easier to manage.
And also realize why the just enough also yeilds a decent result and how a B range will no logner be independent factors on other nutrients due to limitation, not anything to do with speculations about preciptation or interactions.
In fact, adding more may produce a a non limiting higher than expected, since some might get bound up at low dosing leaner levels.

This is why they use nutrient concentration of the plant's dry weight mass % of that nutrient of interest, say Fe.

Here's one of the few papers on the topic with chelated Fe and aquatic foliar uptake:

Basiouny, 1977:
http://www.sciencedirect.com/scienc...serid=10&md5=b80b53b0f9ef5b3517277b47e32d92fa

Regards,
Tom Barr