They may still flick anyway following a partial water change so don't up the de-chlorinator dosage simply on the basis of that. Koi are sensitive to slight chemistry changes in the water and in hard water areas particularly. They'll flash even on my system where tap water is run through three seperate purification filters that remove all the chlorine rather than binding it up as.
If in doubt, why not do away with declor altogether and purify your water instead? You can buy whole house carbon based filteration systems for less than £50.00 so they pay for themselves within a year anyway.
Alan
Posted on Jun 21, 2005, 11:20 AM from IP address 213.120.101.21