drop checker went yello

[phin]

So I've got DIY CO2 set up on my tank. 2 x 124oz gatorade jugs. I get between 2-3 bps. one mix is 16 days old, the other mix is 9 days old. As of last night I was still getting 2+ bps.

My drop checker has been showing a ph of 6.5 for the past week ~38ppm CO2.

Last night, when I got home, I noticed my drop checker was yellow. The lights had been on for about 4 hours, so the plants were photosynthesizing. The 4dkh solution in the drop checker is only a week old. I took the drop checker out of the tank and added a couple drops of my tap water to it. The color instantly turned blue-green, so the pH indicator solution in the drop checker was still good.

I tested the tank water. pH was 6.5, dKH was 4, dGH was 7. All the fish were acting normal, didn't appear stressed or starved for O2.

I refilled the drop checker, put it back in my tank and haven't looked at it since. I forgot to take a look this morning.

Any idea why my CO2 concentration keeps increasing while my DIY CO2 mixes get older?

 

[blert]

Just a few questions...

Size of tank?
Is the CO2 running 24 hours?
Are you assisting out gassing at night? (Air pump on timer, increased surface agitation, etc)
Flow in tank adequate for good mixing?
Position of drop checker in relation to where the CO2 enters the tank?

You could use a valve to regulate BPS. DIY CO2 can be tricky to keep stable.

 

[aqua_chem]

Change anything else in the tank lately? The filter, for instance? It might just be a fluke with this batch of yeast, like accidentally forgetting that you had already add yeast to your mix. I would certainly keep an eye on it though.

 

[phin]

Just a few questions...

Size of tank?
Is the CO2 running 24 hours?
Are you assisting out gassing at night? (Air pump on timer, increased surface agitation, etc)
Flow in tank adequate for good mixing?
Position of drop checker in relation to where the CO2 enters the tank?

You could use a valve to regulate BPS. DIY CO2 can be tricky to keep stable.

Its an 18 gallon tall tank, footprint 10"x20".

CO2 is running 24hrs. I don't increase the surface agitation at night. Originally, I intended to put a air pump on a timer at night, but after I got the drop checker set up I noticed no discernable change in the color of the drop checker at any time during the day. Surface agitation is already quite high with the filtration I already have.

I have a penguin 125 biowheel and a Fluval 206 canister; I've got lots of flow.
CO2 is diffused through an inline reactor right before the water re-enters the tank from the canister. The drop checker is on the glass in the same corner, a few inches below the filter outlet. The CO2-enriched water is blown across the tank, away from the drop checker.

The CO2 concentration in the water doesn't appear to fluctuate from night to day or hour to hour. It appears that I've had a gradual increase in CO2 ppm in the water over the last week.

 

[phin]

Change anything else in the tank lately? The filter, for instance? It might just be a fluke with this batch of yeast, like accidentally forgetting that you had already add yeast to your mix. I would certainly keep an eye on it though.

Nothing else has changed. The thing is, bps has remained pretty constant since I installed the bubble counter/check valve. It makes me think it has more to do with a build up of CO2 in the tank, not a change in CO2 generation.

If my plants are limited by the amount of light they receive, could it be that CO2 builds in the water as the plants are unable to use it, enough and CO2 is unable to diffuse into the air, at a rate equal to or higher than the rate at which CO2 is being added to the water?

I will keep an eye on it and make sure my fish don't appear stressed. If my drop checker constantly stays at yellow I may either drop my water level to create some splashing with my HOB or add a airstone. I may also go from 2 generator jugs to just one.

 

[aqua_chem]

If its been working fine before now, then you should have reached a steady equilibrium. An increase in co2 levels indicates a change in that equilibrium. Your CO2 levels are determined by a dynamic equilibrium, a balance between co2 in and co2 out. CO2 in is almost entirely determined by how much you inject. CO2 out is determined by the rate of plant uptake and the rate of atmospheric loss, with the later being a function of water temperature, surface agitation, and co2 concentration. It's a matter of figuring out what changed in your equilibrium and correcting appropriately, which is admittedly more difficult in DIY setups as you cannot control your co2 in very well.


I guess my somewhat long-winded point is that you might have an accumulation of co2, but its secondary to the actual problem that needs to be identified.

 

[phin]

If its been working fine before now, then you should have reached a steady equilibrium. An increase in co2 levels indicates a change in that equilibrium. Your CO2 levels are determined by a dynamic equilibrium, a balance between co2 in and co2 out. CO2 in is almost entirely determined by how much you inject. CO2 out is determined by the rate of plant uptake and the rate of atmospheric loss, with the later being a function of water temperature, surface agitation, and co2 concentration. It's a matter of figuring out what changed in your equilibrium and correcting appropriately, which is admittedly more difficult in DIY setups as you cannot control your co2 in very well.

I guess my somewhat long-winded point is that you might have an accumulation of co2, but its secondary to the actual problem that needs to be identified.

Water Temperature! We had a cold front come through this week. I actually had to scrape some frost off my windshield monday morning with an old cassette tape (whats that? I know, but they are more common in tallahassee than ice scrapers!).

The temp in my tank has been about 78.4F, however, I noticed this week that my water temp was down to 77.1F. I know its not a huge difference, but these are the numbers I remember seeing when I'd turn the thermometer on and check, so its not like I have a continuous recording of temperature data. It is possible that the temperature has been even lower at times. It has been colder in my house this week ~69-70, usually I'm at 72-74. My heater is a 100W marineland, about 4 years old, so it might not be so quick to keep the temperature real constant.

I'll check the drop checker and water temp when I get home and turn the heater up to closer to 80F if necessary. Thanks!

 

[aqua_chem]

It's possible, but I'm dubious for two reason. One: a one degree temp swing probably won't give you a significant concentration swing. Two: your DIY co2 broth should also have been colder, which would result in markedly less co2 going in, especially considering you're mixture is unheated.

 

[phin]

Thats the only explination that makes sense though. If I was already running high ppm, it might not take too much of a temperature change to increase CO2 concentration just enough to turn the drop checker from a light green to yellow, no?