8.3 sounds awfully high ... is your water very, very, very hard? or very soft maybe? I know Oakland county has rather hard water, but I'm not sure if your area draws from the same aquafir(sp?)
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hard water:
you mentioned driftwood in your tag-line ... the tank the pleco is in has driftwood already? is it real driftwood, or the plastic / composite kind?
try getting some organic peatmoss and putting a little in the next cartridge you rebuild (or just put some in a womens nylon sock and put it in the filter
the peatmoss will soften your water and reduce the PH
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soft water:
someone else's experitise is needed here ... I have no idea on how to bring down the ph of softwater without using chemicals (which could bring it down a LOT)