It's pretty hard to find how to do it (i think the only tutorial was on this forum, and it wasn't very explicit) so i'm gonna help you.
You have to record then use some converters and see what's the packet. you will see that don't change. if i'm not wrong, it's the first octet, and then the 3rd and 4th, or may be the 4th and the 5th.(they are more octets who don't change, but thats the only one we need to use. Then you use a resist potion, and look at the same packet and so you make a filter who changes the 1st octet and the two others (the first octet is here to say that *this packet should be interpreted as "someone uses some consumable somewhere" so you have to keep it, or your filter will apply even when you're skilling/whatever (just make the 1st octet => 1st octet so that wpe checks it has this in the paquet* *the two others say what consummable has been used, (so in fact you say your client the other uses a resist potion whereas he uses a converter) and this for the 4 elements.