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Re: Ph Drifting Down Between Water Changes...

>Date: Sun, 18 Feb 2001 11:51:55 -0500
>From: Paul Mouritsen <mourip at erols_com>
>Subject: Ph Drifting Down Between Water Changes...
>Over the last month or so I have found my average PH to be slowly drifting
>down. It used to be around 6.9 now it is 6.65. Here are some details.
>Tap- ph 8.2, kh 4, gh 8
>Tank- ph 6.65, kh 2, gh 8 (before lights this AM)(changed water yesterday )

Your tank is using alkalinity, buffering capacity or carbonate 
hardness (KH) at a rate you can calculate.   Try adding some 
potassium bicarbonate to raise your KH up closer to or level with 
your hardness (GH).   To raise the KH 10ppm or about half a German 
degree, which I think is the measurement you have used, add 20 grams 
per  cubic meter (1000 litres).   You can use sodium bicarbonate as a 
buffer but plants don't use the sodium.   Potassium bicarbonate will 
provide a potassium source for the plants as well as buffering 
capacity.   Potassium bicarbonate is a bit harder to find than the 
other but worth the extra effort.   Potassium bicarb is also about 10 
times more expensive than sodium bicarb but you don't have to use 
much.   When you add the buffer the pH will rise so you may increase 
the CO2 rate if it is not on auto.   Plants are about 44% carbon dry 
weight once you raise the KH they can get more carbon and will 
probably start bubbling again.

Dave Wilson