Seperating macros from micros

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.

 

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.

 

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.