why micros and macros on different days

[m-man]

i have seen alot of people saying to dose macros and micros on differnet days, and i didn't know why, i thought i saw someting about the iron coming out of solution?,, but when you add one set to the tank, and the other the next day, the first set of ferts is still in the water, so why does it matter?

[hashbaz]

When phosphates are mixed with iron, it can cause the iron to precipitate out of solution, becoming useless to your plants. The idea behind rotating the dosings is that there will be less phosphates the next day.

I personally think that having to rotate the doses must be necessary only on very, very high light tanks. I have 3wpg and dose all my ferts at the same time and only once a week.

[Purrbox]

As hashbaz has mentioned it is to prevent the Iron from precipitating out of the solution by coming into contact with the Phosphate. As I understand it you only need to separate dosing by 4 hours, but at that point most people find it easier to separate dosing by alternating days. We don't yet understand all the ins and outs of why this happens in some situations and not in others. In a severe case you will actually see the Iron precipitaion as a cloud of white power falling out of the solution and dusting everything. In more minor cases you won't see the percipitation by you will see increasing Iron deficiency in your plants over time. I believe that the percipitation is caused by having concentrated amounts of the two chemicals come in contact with eachother, when dosed on alternate days the other chemical is diluted enough to avoid large amounts of precipitation.

I started out dosing both Macros and Traces on the same day. Over time I started seeing Iron deficiency in my plants. Increasing my Trace dosing to twice the recommended amount didn't help at all. Finally I switched to dosing on alternate days and it disappeared within a week. This was enough proof for me.