CO2 Reactor and Drop Checker Question

[csmith]

This weekend I switched to a CO2 reactor on my 20 and set one up for my 55. I have no clue how to properly run these (as in how much CO2 is injected) as I've used the needlewheel method since I started injecting CO2. Can I expect my BPS rate to drastically drop? I've also seen a huge decline in pearling, even though the only thing that has changes is the method of CO2 dispersal. My DC is steady yellow (from lime-ish green with needle wheel) but nothing is dying. I did find one shrimp dead yesterday, but can't really tell if it was CO2 or not as nothing else seemed affected.

Last night I did pull my DC out of the tank to allow it to return to blue (as it never really drops past dark green on its own overnight) and before CO2 was being injected it was back to green. Do I have a bad 4 dKH solution, or is my tank seriously holding that much CO2 overnight?

Any help is appreciated.

 

[Oreo]

Depending on how much surface agitation you have your water could be retaining a good amount of CO2 over night. I use a pH meter as my CO2 reference (granted, not perfect & while it doesn't tell me exactly how much CO2 is in the water it is a good relative reference.) With no CO2 addition for several days my water is between 7.6-7.8 pH. With CO2 addition it drops down to 6.5-6.6pH during the day and after 8 hours of the CO2 being turned off it only gets back to 7.1-7.3pH. Keep in mind that your drop checker will be maybe an hour or so behind my pH meter. I think it's quite possible for your drop checker to be green in the morning and still be functioning properly.

 

[hbosman]

You might want to back off your bubble rate a little until you see some green. Otherwise, you won't be able to tell if there is any increase in CO2 saturation if its' already yellow.

 

[scottward]

Depending on how much surface agitation you have your water could be retaining a good amount of CO2 over night.

No, I don't this is true. The water will fairly rapidly 'want' to reach equilibrium with the air. If the water retained CO2 in this way life would be much easier for us in terms of getting CO2 into the water in the first place. Once the CO2 is off, the level of CO2 should drop fairly quickly.

csmith, I would forget about the drop checker. Throw it out. ;-)

How do your plants look? Observe them over a week. If they start to loose their luster, growth slows down etc, turn up the CO2 a *tiny* bit and keep a close eye on the tank. If the fish start to head for the surface, back off the CO2.

 

[Whiskey]

Well,.. I don't think that's a very good idea - a Drop checker can be a great tool to get you in the ballpark - sure observing the plants can help you fine tune things, but it takes much less time to get to a point where you are fine tuning when your using tools like a dropchecker. I would trust it's readout and tune your CO2 system using it for starters just like you did when you first setup the needlewheel system.

Depending on your fish load, plant load, and the amount of surface agitation, your tank could easily have 10 PPM of CO2 when the lights switch on. At night the fish are still making CO2, and if memory serves even the plants make a little bit of CO2 without the lights on,.. with no surface agitation especially if there is a film on the top it can add up.

HTH,
Whiskey

 

[csmith]

There is plenty of surface agitation. What isn't moving because of filter output is moving because of a powerhead. Observation for the day: 1 BPS with this reactor keeps my DC yellow throughout the day, whereas with the needle wheel I think it took 4-5 BPS. I'll have to back it down quite a bit more.

 

[Oreo]

No, I don't this is true. The water will fairly rapidly 'want' to reach equilibrium with the air. If the water retained CO2 in this way life would be much easier for us in terms of getting CO2 into the water in the first place. Once the CO2 is off, the level of CO2 should drop fairly quickly.

Here's an example for you then... crack open a can of soda before you go to bed. When you wake up, taste the soda. It will still be fairly well carbonated, even at room temperature. Water reaching equilibrium does take time. There are two other things to consider here... First, the relationship of pH to CO2 concentration isn't linear. The closer the water gets to equilibrium the less the change in pH. (A drop checker is essentially a pH test.) Second, think of water off-gassing CO2 similar to a chemical half-life. For instance, (I'll just make up a number here) lets say what ever the CO2 content of the water is, 50% will off-gas in 2 hrs. That means that after 2 hrs you have 1/2 the original CO2 content, and 2 hrs after that you have 25% the original CO2 content. 2hrs later 12.5%, etc. The absolute rate in terms of ppm of CO2 off-gassed per minute gets slower as the CO2 concentration decreases. Combine this with the non-linear pH effect on the drop checker solution, not to mention the 2hr delay on the drop checker's function and you could easily have a drop checker still reading green in the morning.

 

[scottward]

Ah ok. I always thought that CO2 left fairly rapidly (i.e. within a couple of hours) to reach equilibrium. I suppose a can of soda has a much smaller surface area though - whereas the typical aquarium, with much larger surface area, would degass faster. Soft drink (what aussies call soda) always seems to go flat on me pretty quickly - by the next morning it would be as flat as a strap for me. ;-)