Zodiark isn't hard per se, only in the part where he puts the paling and magick shield on. The main problem with him, is that he tends to spam Darkja at will, which has a 50% chance of instant death or 25% if you equipped Demon Shields on your chars, and sometimes he would use it 5 times in a row.
With Paling and Magick Shield he was invulnerable to your attacks most of the time, except for a small window of opportunity where the magick shield went down for a few seconds, which you could bombard him with Shock or use a Quickening in which if you were lucky enough, you would kill him in one go. While this window of opportunity didn't appear, you would have to stand up to him casting Shock, Scourge (not Purge, sorry for before), Scathe and Darkja.
So you see, it wasn't hard per se, it was more a matter of sheer luck.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"
