Last week I finally scrounged up enough change to get a fully automated CO2 setup. With the cylinder in place, probe in the water and pH dialed in I turned everything on and it works like a charm.

Well, almost. The KH just keeps going higher and higher. I set the system to a pH of 6.8. It's not been a week and the KH has gone from 4 to almost 9! Due to this higher alkalinity it's been harder and harder for the system to get the pH down to 6.8. Tonight it was at 6.9 and checking the chart, that means the CO2 is around 33ppm. I really don't want it above 30ppm.

So my question to those of you who have fully automated CO2 system is how do you maintain the right pH to KH? Do you slowly raise the target pH on your system's dial over the corse of time? What about sky rocketing KH? How do you balance all these things? I guess partial water changes are really important now to help restore a more normal KH. I'm just wondering what routines some of you do - what's worked for you.

Until I find a balance for things, I'll be keeping an eye out for any fish sucking air at the surface. . .

Where to begin?

First, I guess, the KH. If your KH is going up that much you most likely have some carbonate rocks or gravel in the tank. If you don't want the rising KH you have to get rid of those carbonate sources.

Second, the pH/KH relationship. The charts of ppm of CO2 vs pH and KH are good only if you know that nothing in your water affects the pH except the CO2, and nothing affects the KH except carbonates. Very rarely will our tank water meet those requirements. That means the table is worthless for measuring CO2 in a tank of typical aquarium water.

Last, it isn't the pH that is important for either the fish or the plants. It is the concentration of CO2 in the water (too high kills the fish - too low stops plant growth and starts algae growth), and the TDS (total dissolved solids) in the water, which are measurable to some extent by measuring KH and GH.

If you get a drop checker and fill it with 4 dKH distilled or deionized water you can find out if you have enough CO2 in the water, or too much or too little. Without spending a lot more money or having a lot more experience you can't determine that any other way.

I also purchased the equipment for a fully automated CO2 setup a while back and quickly realized life is much easier if you just turn the CO2 on when the lights go on and turn it off when the lights go off. I still use the controller but it acts only as a monitor for the PH, not a controller (anybody out there want to swap a Pinpoint pH controller for a digial pH monitor?)

IMHO there are just too many things that can affect pH to use it as a control method for CO2 dosing.

Easiest way is to get a dropchecker (DC) with a kh 4.0 solution and have a beetlecounter and a good needlevalve for fine addjustment.

Turn on the CO2 and at midday watch the DC Then adjust the bubbles if you got too much or not and observe the DC the next day ect. Adjusting too much dont help since the DC dont respond so fast, and its also good to only read the DC each day at about the same time.

I see. That's a shame - the pH controller is the most expensive part of the CO2 setup! Looks like I'll have to get a timer. The thing that's getting me is that I always have to open the flow valve on the CO2 more every day. I mean, it can't be losing that much pressure over 24 hours. I find if I don't have two bubbles per second, the pH is going to go up. At 2bps it holds the pH steady - it's just that the flow slows to 1bps or lower all too quickly. Quite agravating given the amount I paid for the pressure valve/bubble counter/solenoid combo.

On a completely different front, I recently took a chance and got a few zebra loaches (botia striatus). They seem to be tearing up the grass species I have (microsword, dwarf helzine). I like loaches and especially the zebras, but they might have to go. . .