expect the output to have low ph, its not perminent and only requires gas
exchange to
bring the ph back up to what the tank level is.

I'm interested in this....as per my other post, what I have found (tested)
is that the water coming out the Nitrate filter has a very much Lower Kh
than when it went in. This would explain why the Ph is lower since Kh & ph
run in the same direction given a constant level of CO2. What I'm not sure
of though is that the change is only temporary (or why its happening at
all!) - but it seems pretty permanent from what I've found - i.e. over the
course of a week to 10 days the Kh in my tank dropped away quite
considerably. I am intersted to know however as to whether this will be a
permanent side effect of using the Nitrate filter or does the effect on Kh
become less severe as the flow rate through the denotrator is increased?

rgds

Iain