[cS]

Ethan,

I just saw those pictures of yours in the "propagating E. cinereum" thread and it reminded me of this thread. What kind of substrate are you using? Is it Flora Base or ADA soil? I am suspecting that it is what's consuming your KH.

 

[cS]

I'd bet that the Flora Base is causing the KH drop. Flora Base contains an acid buffer and it acts similarly to peat: exchanging Ca++/Mg++ ions for H+ ions that bind with the bicarbonates, thus lowering your KH (and GH).

Such a noticeable drop in KH from a non-carbonate buffer would make your CO2 calculations misleading.