That might sound like a silly question for the scientific type of person, but I was just wondering why it is recommended to mix the dry ferts in distilled water, instead of tap water? Or should I rather ask, could that be the reason my tank water has always been "milky", specially after dosing?

Also I have read it is not recommended to dose Fe & PO4 on the same day... Why?
(just trying to learn here...)

I don't, I usually use tap, except for the traces if they happen to be dry mix.......
The KH can affect the chelator, so less is better.

Regards,
Tom Barr

If you mix the iron solution with the phosphate solution the iron combines with the phosphate to form a precipitate - clouds the water temporarily until the precipitate settles on the substrate. If you do this in a premix of all ferts it is serious, because none of the fert doses will contain the expected amount of iron and phosphate. If you do it by dumping the dry powder into the tank, it just temporarily removes those ferts from being available to the plants. Eventually the precipitate will be consumed as a substrate fertilizer. So, those who sell ferts always say don't dose both at once, and don't try to mix up all of the daily ferts in one bottle.

That would explain it. Thanks guys!

Tom's comment about KH is also part of the reason why you will often see one person preferring Flourish or TMG (or whatever its name is this month <g>) or Plantex CSM ... each will perform slightly differently in my tank than they will in yours ...

Historically, Tom has usually preferred the old TMG over Flourish, where I have always preferred Flourish (if I was going to use a commercial micro nutrient) ...

Greg