is there mg in plantex? if not how can i add some to the tank? thanks

No, MgSO4, epsom salt, is part of the old PMDD recipe along with KNO3 that folk's added to Plantex, as well as boric acid for boron.

You can simply use epsom salt to your recipe.
It's about 79 cents for 2 liters worth.

Regards,
Tom Barr

how much should i add? am using EI, and am having few holes in the leaves, co2 on target with dc 4kh.
how much mg should i add and how often?
thanks

You can mix it into the trace mix.
See here:

Practical PMDD Information

As you can see, EI/PMDD and the other incarnations go back well over a decade.

Few folks refer to PMDD much these days and even fewer used PMDD in the original form.

So a 1:1 ratio of MgSO4 should suffice with plantex.

So dose 2-3x a week etc like the traces.
You can likely dose once a week also after a water change.

Some bozos claim dosing it carefully daily helps their plants.
I've never seen this(I tried that) and I have little trouble growing any plant dosing Mg once a week........so that's the control that shows it's not really doing much and that some other thing is giving their results...........

You repeat it a few times, then it's pretty plain.

Regards,
Tom Barr