chromatic doom, help needed Options

[Kerkes]

I need some help with chromatc demon. My party is: riskbreaker lvl 21 - long sw +3 and equlizer
valygar lvl 19 - +3 club and +4 shortswrd
ber-cler 9-21 - foa+3, flail+3
ber-mag 9 -18 staff+3
imoen 19
cernd 17
I usually did this with more fighters and the fight was easy. But now I have only two, since my cleric must heal. Imoen seems not to be able to hurt him with adhws after firing 3xlower resistance trigger (she has vecna). Cernd, on the other hand, does wonders with his aura clensing and unleash energy. Isn't that the same kind of damage(magic)? why doesn't adhw work? I don't get any message about what's happening. Yet unleash energy does not seem to be enough (does 20-25dmg) , demon gets "near death" but that's as far as he'll get. As soon as Cernd is out of unleash (he has 6 or 7 I believe), I may as well reload. I've also tried magic missile under imp.alcatry (does nothing) , waiting for demon to switch to ice form so that flame arrows hurt him, but he killed my spellcasters before that etc. Any hints? In his red demon form, how can I hurt him with elements? I just hope it's not ice. I also don't get any message for bolt of glory.

[Kerkes]

Well, it's all over now. Cernd was the big winner, delivering over 100 points of damage to good old chrom. I loaded my mage with spell trigger 3xice storm, spell seq.also, rest, save, buff up, kill the damn thing. Too bad Imoen doesn't know ice storm.
tnx for advice on ice storm! A bit weak, but with 9 of them in the air, it adds up.
I agree with the statments above about weak ice and acid spells. They're ridiculusly weak compared to simple flame arrow. Cone of cold is good, but hard to use sometimes. And if it kills someone, he will break into pieces.