I dipped my hand into my tank to repair the slight damaged done by SAEs that uprooted my Glosso. After about a minute or so, my arms felt quite itchy.

When done, I washed my hand and the itchiness are gone. Could it be Nitrite?

This is a 700L tank with about 600L of water in it. I used 2 units of Eheim 2228 with the standard media for filters: Filter Pad, Eheim Substrat Pro, Foam Pad and Ehfimech. But they have been serving me for the past 10 years. Do I need to change those media ?

No, that's a critter, search the Aquatic Plant's digest, I think it's a little bug etc, or you might be allergic to something else.

It's not due to NH4, NO2 etc.....

Regards,
Tom Barr