There are other spells he can request of his [god]. Going through those requests one to a day is what's slowing them down, but there are plenty more things to try.
Esta is still using Tongues and Cultural Adaptation once per day, and he has picked up the general impression that sane people do not fuck around with the 'radioactivity' business. How about if today's keeping of Heal is expended on Merrin, who has been to a cave that has supposedly not set off her radiation detectors?
Actually, at some point after testing Greater Make Whole on other Dark Tapestry 'dath ilani technology', they should apply it to Merrin's allegedly nonmagical armor. In case some part of it has spontaneously stopped working, as 'technology' sometimes does. Some part like the 'radioactivity' detectors, for example.
(There are in fact things in Golarion that sound as scary as radioactivity sounds in Baseline, treated as seriously as Cultural Adaptation says a dath ilani should treat 'radioactivity'. Shoggoths, for example. Or Lilitu. Cheliax takes those about as seriously as dath ilani takes 'radioactivity' from sources like 'radon'. Such are the hazards of trying to match cross-cultural scales of danger based on prioritized concern; some cultures do in fact have worse things to worry about than others.)