"jet" wrote in message
oups.com...
I recently added a pressurized CO2 system to my 38 gal aquarium. I use
RO water and added calcium carbonate to obtain 4 KH and 4 dGH. The pH
initial shot up to 8.5 (from 7.2) and then dropped to 7.6 overnight.
When I got home from work it was down to 7.4 and has not moved in the
16 hours since then. Is this typical?

Here is the system:
Aquamedic CO2 Reactor 500
Milwaukee SMS122 pH Controller
Milwaukee MA957 Regulator
Eheim 2011 to provide the current

The 2011 and an additional 2213 are using 2 Eheim surface extractors.
Neither filter's discharge is directed at the surface. There are no air
stones either. So there should not be much CO2 stripping going on. I'm
using a 96wt 5700K compact light and the tank it moderate to heavily
planted. Substrate is a quartz sand/laterite mix.

Is there any obvious reason the pH is being so stuborn?

Your description seems to have the answer

The calcium carbonate is diffusing faster because of the carbonic acid
coming from the CO2. 7.4 is probably the balance between the carbonic acid
and calcium carbonate. As the calcium carbonate levels drop, so will the pH.

How is your hardness dealt with? Are you adding powdered calcium carbonate,
or do you filter over coral or something?

If you are adding by hand then 7.4 looks like it will be about where your
CO2 pH will be. If it's a more sedentry type of buffering, then as it
weakens over time, so the pH, buffering and hardness will drop. Be careful
of pH crashing in any case.


Oz

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My Aquatic web Blog is at http://members.optusnet.com.au/ivan.smith