Iron precipitation

I am in a coco DTW system. Having problems with iron precipitating out. I say iron… as it is black but I haven’t tested if it is magnetic. Just occurred to me.
Regardless, black precipitate in my reservoir. Here’s the recipe I am following:


GH Armor Si 3ml/gal
Peters 3.4g/gal
Calcinit 2.3g/gal
Epsom 1.2g/gal
Greenway Cal-Mag powder reconstituted per directions 3ml/gal

I know the cal-mag and Si are not typical in a 3-2-1 setup but I won’t stop using Si because it makes a huge difference.
The cal-mag is added as my plants continue to require more calcium and I was reluctant to just use more calcinit. I am not super familiar with the whole 3-2-1 as I have just recently left my four year affair of liquids. I am super familiar with this cal-mag preparation.

So, thoughts on the black precipitate?

first i'd figure out what it is and then figure out what would cause it to precipitate out of solution

iv'e never heard of iron doing that.

The order in which you mix the nutrients can cause elements to precipitate out of suspension. I run Si and Jack's 3-2-1. I always add Si to my RO water first. Once well mixed I then add Jack's part A, then Epsom, then part B calnit. Always making sure each component is well mixed before adding the next. On the rare occasions when I do use CalMag I add it last. I've never had any precipitation problems .