Adding CO2 after fish....

[Matt W]

OK...so I've changed my mind about adding CO2 to my tank. At first I thought I would go low light and not worry about CO2. Well, I wasn't happy with plant growth and upgraded the lights. I am now sitting at almost 3 watts per a gallon. So, I decided to go 'whole hog' and get pressurized CO2.

I should have the regulator delivered on Wednesday, and I already have a tank filled and ready to go. My plan is to start with a _very_ small amount of CO2 and work my way to where I want to be.

This will be going on a 125 gallon with a kH of 125.3ppm, pH of 7.6, which gives me about 5ppm of CO2. I want to get it to about 20ppm which would be a pH of 7.0. Can anyone suggest how many bubbles per minute (second) I would need? How quickly can I drop down to 7.0pH without freaking the fish out?

One other question. What is the best way to deal with water changes in a tank with CO2? Obviously the water coming in won't be the same pH. Will just doing small frequent changes (2-3 times a week) be enough to minimize the impact?

Thanks in advance!

[RTR]

Nobody can predict the CO2 concentration in a particular tank from the bubble rate - it is unique to each setup, the use rate, the blowoff, the reactor or whatever dissolving technique is used, etc. Just start slow and check. Under-supplementing during adjustment is conservative, over-dosing has hazards.

When you think you are where you want to be, check just at or before lights on (highest CO2/lowwest pH) and just before lights off (lowest CO2/highest pH). Most equipment is pretty stable except for large temperature swings in the room (non-AC summer afternoons versus cold winter nights), and even that has a lag.

[djlen]

Agree with RTR entirely. Close watching of pH is necessary for the first few days to see how your water reacts to the amount of CO2 injected.
You can start with a bubble rate of 1 bubble every 2 secs. and go from there without any danger as long as you check pH every hour or two. A good needle valve will allow you to be very precise in your dosing.
As to the pH swing when doing water changes. I do a 40 - 50% water change every week and notice no appreciable swing in pH and if there is a slight swing, it stabilizes quickly. The fish will swim right into the incoming water. This btw, is in a tank that is kept at 6.4 and has 7.4pH tap water being introduced. I would be more concerned regarding water temp and making sure you are adding tap water conditioner as the the fresh water is going into the tank.

Len